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4nts  and  Some  Other  Insects 

An  Inquiry  into 

The  Psychic  Powers  of  these  Animals 

With  an  Appendix  on 

The  Peculiarities  of  Their  Olfactory  Sense 


By 

Dr.  August  For  el 

Late  Professor  of  Psychiatry  at  the  University  of  Zurich 


/4.48S 

Translated  from  the  German 

By* 
Prof.   William  Morton  Wheeler 

American  Museum  of  Natural  History,  Neva  York 


Chicago 
The  Open  Court  Publishing  Company 

London 

Kegan  Paul,  Trench,  Trubner  &>  Co.  Ltd. 
'9°4 


1906 


COPYRIGHT,  1904 
THE  OPEN  COURT  PUBLISHING  CO. 

CHICAGO 


.    • 

V 

ANTS  AND  SOME  OTHER  INSECTS. 

74488 

WHEN  discussing  the  ant-mind,  we  must  consider  that  these 
small  animals,  on  the  one  hand,  differ  very  widely  from  our- 
selves in  organisation,  but  on  the  other  hand,  have  come,  through 
so-called  convergence,  to  possess  in  the  form  of  a  social  common- 
wealth a  peculiar  relationship  to  us.  My  subject,  however,  requires 
the  discussion  of  so  many  complicated  questions  that  I  am  com- 
pelled to  assume  acquaintance  with  the  work  of  others,  especially 
the  elements  of  psychology,  and  in  addition  the  works  of  P.  Huber, 
Wasmann,  von  Buttel-Reepen,  Darwin,  Romanes,  Lubbock,  my 
Fourmis  de  la  Suisse,  and  many  others.  Since  the  functions  ot  the 
sense-organs  constitute  the  basis  of  comparative  psychology,  I 
must  also  refer  to  a  series  of  articles  entitled  "Sensations  des  In- 
sectes"  which  I  have  recently  published  (1900-1901)  in  the  Rivista 
de  Biologia  Generate,  edited  by  Dr.  P.  Celesia.  In  these  papers  I 
have  defined  my  position  with  respect  to  various  authors,  especially 
Plateau  and  Bethe. 

Very  recently  Bethe,  Uexkull,  and  others  have  denied  the  ex- 
istence of  psychic  powers  in  invertebrate  animals.  They  explain 
the  latter  as  reflex-machines,  and  take  their  stand  on  the  ground  of 
the  so-called  psycho-physical  parallelism  for  the  purpose  of  demon- 

•^  strating  our  inability  to  recognise  mental  qualities  in  these  animals. 

s.  They  believe,  however,  that  they  can  prove  the  mechanical  regu- 
larity of  behavior,  but  assume  unknown  forces  whenever  they  are 
left  in  the  lurch  in  their  explanations.  They  regard  the  mind  as 
first  making  its  appearance  in  the  vertebrates,  whereas  the  old  Car- 
tesians regarded  all  animals,  in  contradistinction  to  man,  as  mind- 
less (unconscious)  machines. 


2  ANTS  AND   SOME  OTHER   INSECTS. 

The  Jesuit  father  E.  Wasmann  and  von  Buttel-Reepen  are 
willing,  on  the  other  hand,  to  accept  the  inductive  inference  from 
analogy  as  a  valid  scientific  method.  Like  Lubbock,  the  lecturer 
and  others,  they  advocate  a  comparative  psychology  of  the  inverte- 
brates and  convincingly  demonstrate  the  existence  of  psychic  facul- 
ties in  these  animals.  Wasmann,  however,  puts  a  very  low  esti- 
mate on  the  mental  powers  of  the  higher  vertebrates  and,  in  my 
opinion,  improperly,  denies  to  them  any  ability  of  drawing  infer- 
ences from  experience  when  in  the  presence  of  new  conditions  (this 
alone  he  designates  as  intelligence) ;  he  believes  that  man  alone 
possesses  an  immortal  soul  (independent  of  natural  laws  ?)  in  addi- 
tion to  the  animal  mind. 

It  is  necessary,  first  of  all,  to  arrive  at  some  common  under- 
standing concerning  the  obscure  notion  "psychic"  in  order  that 
we  may  avoid  logomachy,  and  carrying  on  theology  in  the  sense  of 
Goethe's  Mephistopheles.  Two  concepts  are  confounded  in  an 
obscure  manner  in  the  word  "psychic"  :  first,  the  abstract  concept 
of  introspection,  or  subjectivism,  i.  e.,  observation  from  within, 
which  every  person  knows  only,  and  can  know  only,  in  and  by  hinir 
self.  For  this  let  us  reserve  the  term  "consciousness."  Second, 
the  "activity"  of  the  mind  or  that  which  determines  the  contents 
of  the  field  of  consciousness.  This  has  been  included  without  fur- 
ther ado  with  consciousness  in  the  wider  sense,  and  thence  has 
arisen  the  confusion  of  regarding  consciousness  as  an  attribute  of 
the  mind.  In  another  place  I  have  designated  the  molecular  wave 
of  activity  of  the  neural  elements  as  "neurocyme. " 

We  cannot  speak  of  the  consciousness  of  human  beings  other 
than  ourselves  without  drawing  an  inference  from  analogy ;  quite 
as  little  ought  we  to  speak  of  a  consciousness  of  forgotten  things. 
The  field  of  our  consciousness  is  constantly  changing.  Things  ap- 
pear in  it  and  disappear  from  it.  Memory,  through  association, ' 
enables  us  to  recall,  more  or  less  directly  and  with  more  or  less  diffi- 
culty, things  which  appear  to  be  momentarily  absent  from  con- 
sciousness. Moreover,  both  the  experience  of  self-observation  and 
the  phenomena  of  hypnotism  teach  us  experimentally  that  many 
things  of  which  we  seem  to  be  unconscious,  are  nevertheless  pres- 


ANTS  AND  SOME  OTHER  INSECTS.  3 

ent  in  consciousness  or  have  been.  Indeed,  certain  sense-impres- 
sions remain,  at  the  moment  of  their  occurrence,  unconscious  so 
far  as  our  ordinary  consciousness  or  superconsciousness  is  con- 
cerned, although  they  can  be  subsequently  recalled  into  conscious- 
ness by  suggestion.  Whole  chains  of  brain-activities,  (dreams, 
somnambulism,  or  secondary  consciousness)  seem  ordinarily  to  be 
excluded  from  the  superconsciousness,  but  may  subsequently  be 
associated  by  suggestion  with  the  remembered  contents  of  con- 
sciousness. In  all  these  cases,  therefore,  what  seems  to  be  uncon- 
scious is  after  all  proved  to  be  conscious.  The  above-mentioned 
phenomena  have  frequently  led  to  mystical  interpretations,  but 
they  are  explainable  on  a  very  simple  assumption.  Let  us  assume 
— and  this  is  quite  in  harmony  with  observation — that  the  fields  of 
the  introspectively  conscious  brain-activities  are  limited  by  so-called 
association  or  dissociation  processes,  i.  e.,  that  we  are  unable  ac- 
tively to  bring  them  all  into  connection  at  the  same  time,  and  that 
therefore  all  that  seems  to  us  unconscious  has  also  in  reality  a  con- 
sciousness, in  other  words,  a  subjective  reflex,  then  the  following 
results :  Our  ordinary  waking  consciousness  or  superconsciousness 
is  merely  an  inner  subjective  reflex  of  those  activities  of  attention 
which  are  most  intimately  connected  with  one  another,  i.  e.,  of  the 
more  intensively  concentrated  maxima  of  our  cerebral  activities 
during  waking.  There  exist,  however,  other  consciousnesses,  partly 
forgotten,  partly  only  loosely  or  indirectly  connected  with  the  con- 
tents of  the  superconsciousness,  in  contradistinction  to  which  these 
may  be  designated  as  subconsciousness.  They  correspond  to  other 
less  concentrated  or  otherwise  associated  cerebral  activities.  We 
are  bound  to  assume  the  existence  of  still  more  remotely  intercon- 
nected subconsciousnesses  for  the  infra-cortical  (lower)  brain- 
centers,  and  so  on. 

It  is  easy  to  establish  the  fact  that  the  maximum  of  our  psychic 
activity,  namely,  attention,  passes  every  moment  from  one  percep- 
tion or  thought  to  another.  These  objects  of  attention,  as  visual 
or  auditory  images,  will-impulses,  feelings  or  abstract  thoughts, 
come  into  play — and  of  this  there  is  no  doubt — in  different  brain- 
regions  or  neuron-complexes.  We  can  therefore  compare  attention 


4  ANTS  AND   SOME  OTHER  INSECTS. 

to  a  functional  macula  lutea  wandering  in  the  brain,  or  with  a  wan- 
dering maximal  intensity  of  neurocymic  activity.  But  it  is  quite  as 
satisfactorily  established  that  other  psychic  phenomena  external  to 
attention  are  likewise  present  in  consciousness,  though  in  a  feebler 
condition.  Finally,  it  is  well  known  that  all  that  has  been  in  con- 
sciousness— even  that  which  is  now  more,  now  less,  forgotten — is 
included  in  the  psychic,  i.  e.,  in  the  contents  of  consciousness.  On 
superficial  consideration  this  appears  to  satisfy  theoretical  require- 
ments. But  in  fact  and  in  truth  there  are  innumerable  processes 
of  which  we  are  feebly  conscious  for  only  a  scarcely  appreciable 
instant  and  which  anon  disappear  from  consciousness.  Here  and 
not  in  the  strong  and  repeated  "psychomes" — I  beg  your  indul- 
gence for  this  word,  with  which  I  would  for  the  sake  of  brevity 
designate  each  and  every  psychic  unit — are  we  to  seek  the  transi- 
tion from  the  conscious  to  the  apparently  unconscious.  Even  in 
this  case,  however,  the  feeble  condition  of  consciousness  is  only 
apparent,  because  the  inner  reflex  of  these  processes  can  merely 
echo  faintly  in  the  field  of  a  strongly  diverted  attention.  This, 
therefore,  in  no  wise  proves  that  such  half  conscious  processes  are 
in  and  for  themselves  so  feebly  represented  in  consciousness,  since 
a  flash  of  attention  is  sufficient  subsequently  to  give  them  definite 
shape  in  consciousness.  Only  in  consequence  of  the  diversion  of 
the  attention  do  they  lose  more  and  more  their  connection  with  the 
chain  of  intensity-maxima  which,  under  ordinary  circumstances, 
constitute  the  remembered  contents  of  our  superconsciousness. 
The  more  feebly,  however,  they  are  bound  to  the  latter,  with  the 
more  difficulty  are  such  half-conscious  processes  later  associated 
anew  through  memory  with  the  dominant  chain.  Of  such  a  nature 
are  all  dreams,  all  the  subordinate  circumstances  of  our  lives,  all 
automatised  habits,  all  instincts.  But  if  there  exists  between  the 
clearly  conscious  and  the  unconscious,  a  half-conscious  brain-life, 
whose  consciousness  appears  to  us  so  feeble  merely  on  account  of 
the  deviation  of  our  ordinary  train  of  memories,  this  is  an  unequiv- 
ocal indication  that  a  step  further  on  the  remaining  connection 
would  be  completely  severed,  so  that  we  should  no  longer  have  the 
right  to  say  that  the  brain-activities  thus  fading  away  nebulously 


ANTS  AND  SOME  OTHER  INSECTS.  5 

from  our  superconsciousness  do  not  have  consciousness  in  and  for 
themselves.  For  the  sake  of  brevity  and  simplicity  we  will  ascribe 
subconsciousness  to  these  so-called  unconscious  brain -processes. 

If  this  assumption  is  correct — and  all  things  point  in  this  di- 
rection— we  are  not  further  concerned  with  consciousness.  It  does 
not  at  all  exist  as  such,  but  only  through  the  brain-activity  of  which 
it  is  the  inner  reflex.  With  the  disappearance  of  this  activity,  con- 
sciousness disappears.  When  the  one  is  complicated,  the  other, 
too,  is  complicated.  When  the  one  is  simple,  the  other  is  corre- 
spondingly simple.  If  the  brain-activity  be  dissociated,  conscious- 
ness also  becomes  dissociated.  Consciousness  is  only  an  abstract 
concept,  which  loses  all  its  substance  with  the  falling  away  of 
"conscious"  brain-activity.  The  brain-activity  reflected  in  the 
mirror  of  consciousness  appears  therein  subjectively  as  a  summary 
synthesis,  and  the  synthetical  summation  grows  with  the  higher 
complications  and  abstractions  acquired  through  habit  and  prac- 
tice, so  that  details  previously  conscious  (e.  g.,  those  involved  in 
the  act  of  reading)  later  become  subconscious,  and  the  whole  takes 
on  the  semblance  of  a  psychical  unit. 

Psychology,  therefore,  cannot  restrict  itself  merely  to  a  study 
of  the  phenomena  of  our  superconsciousness  by  means  of  intro- 
spection, for  the  science  would  be  impossible  under  such  circum- 
stances. Everybody  would  have  only  his  own  subjective  psychol- 
ogy, after  the  manner  of  the  old  scholastic  spiritualists,  and  would 
therefore  be  compelled  to  doubt  the  very  existence  of  the  external 
world  and  his  fellow-men.  Inference  from  analogy,  scientific  in- 
duction, the  comparison  of  the  experiences  of  our  five  senses,  prove 
to  us  the  existence  of  the  outer  world,  our  fellow-men  and  the  psy- 
chology of  the  latter.  They  also  prove  to  us  that  there  is  such  a 
thing  as  comparative  psychology,  a  psychology  of  animals.  Finally 
our  own  psychology,  without  reference  to  our  brain^activity,  is  an 
incomprehensible  patchwork  full  of  contradictions,  a  patchwork 
which  above  all  things  seems  to  contradict  the  law  of  the  conser- 
vation of  energy. 

It  follows,  furthermore,  from  these  really  very  simple  reflections 
that  a  psychology  that  would  ignore  brain-activity,  is  a  monstrous 


6  ANTS  AND  SOME  OTHER   INSECTS. 

impossibility.  The  contents  of  our  superconsciousness  are  con- 
tinually influenced  and  conditioned  by  subconscious  brain-activi- 
ties. Without  these  latter  it  can  never  be  understood.  On  the 
other  hand,  we  understand  the  full  value  and  the  ground  of  the 
complex  organisation  of  our  brain  only  when  we  observe  it  in  the 
inner  light  of  consciousness,  and  when  this  observation  is  supple- 
mented by  a  comparison  of  the  consciousness  of  our  fellow-men  as 
this  is  rendered  possible  for  us  through  spoken  and  written  lan- 
guage by  means  of  very  detailed  inferences  from  analogy.  The 
mind  must  therefore  be  studied  simultaneously  from  within  and 
from  without.  Outside  ourselves  the  mind  can,  to  be  sure,  be 
studied  only  through  analogy,  but  we  are  compelled  to  make  use  of 
this  the  only  method  which  we  possess. 

Some  one  has  said  that  language  was  given  to  man  not  so 
much  for  the  expression  as  for  the  concealment  of  his  thoughts.  It 
.is  also  well  known  that  different  men  in  all  honesty  attribute  very 
different  meanings  to  the  same  words.  A  savant,  an  artist,  a 
peasant,  a  woman,  a  wild  Wedda  from  Ceylon,  interpret  the  same 
words  very  differently.  Even  the  same  individual  interprets  them 
differently  according  to  his  moods  and  their  context.  Hence  it 
follows  that  to  the  psychologist  and  especially  to  the  psychiatrist — 
and  as  such  I  am  here  speaking — the  mimetic  expression,  glances 
and  acts  of  a  man  often  betray  his  true  inner  being  better  than  his 
spoken  language.  Hence  also  the  attitudes  and  behavior  of  ani- 
mals have  for  us  the  value  of  a  "language,"  the  psychological  im- 
portance of  which  must  not  be  underestimated.  Moreover,  the 
anatomy,  physiology  and  pathology  of  the  animal  and  human  brain 
have  yielded  irrefutable  proof  that  our  mental  faculties  depend  on 
the  quality,  quantity,  and  integrity  of  the  living  brain  and  are  one 
with  the  same.  It  is  just  as  impossible  that  there  should  exist  a 
human  brain  without  a  mind,  as  a  mind  without  a  brain,  and  to 
every  normal  or  pathological  change  in  the  mental  activity,  there 
corresponds  a  normal  or  pathological  change  of  the  neurocymic  ac- 
tivity of  the  brain,  i.  e.,  of  its  nervous  elements.  Hence  what  we 
perceive  introspectively  in  consciousness  is  cerebral  activity. 

As  regards  the  relation  of  pure  psychology  (introspection)  to 


ANTS  AND  SOME  OTHER  INSECTS.  7 

the  physiology  of  the  brain  (observation  of  brain-activity  from  with- 
out), we  shall  take  the  theory  of  identity  for  granted  so  long  as  it 
is  in  harmony  with  the  facts.  The  word  identity,  or  monism,  im- 
plies that  every  psychic  phenomenon  is  the  same  real  thing  as  the 
molecular  or  neurocymic  activity  of  the  brain-cortex  coinciding 
with  it,  but  that  this  may  be  viewed  from  two  standpoints.  The 
phenomenon  alone  is  dualistic,  the  thing  itself  is  monistic.  If  this 
were  otherwise  there  would  result  from  the  accession  of  the  purely 
psychical  to  the  physical,  or  cerebral,  an  excess  of  energy  which 
would  necessarily  contradict  the  law  of  the  conservation  of  energy. 
Such  a  contradiction,  however,  has  never  been  demonstrated  and 
would  hold  up  to  derision  all  scientific  experience.  In  the  mani- 
festations of  our  brain-life,  wonderful  as  they  undoubtedly  are, 
there  is  absolutely  nothing  which  contradicts  natural' laws  and  jus- 
tifies us  in  postulating  the  existence  of  a  mythical,  supernatural 
"psyche." 

On  this  account  I  speak  of  monistic  identity  and  not  of  psycho- 
physical  parallelism.  A  thing  cannot  be  parallel  with  itself.  Of 
course,  psychologists  of  the  modern  school,  when  they  make  use  of 
this  term,  desire  merely  to  designate  a  supposed  parallelism  of 
phenomena  without  prejudice  either  to  monism  or  dualism.  Since, 
however,  many  central  nervous  processes  are  accessible  neither  to 
physiological  nor  to  psychological  observation,  the  phenomena  ac- 
cessible to  us  through  these  two  methods  of  investigation  are  not 
in  the  least  parallel,  but  separated  from  one  another  very  unequally 
by  intermediate  processes.  Moreover,  inasmuch  as  the  dualistic 
hypothesis  is  scientifically  untenable,  it  is  altogether  proper  to 
start  out  from  the  hypothesis  of  identity. 

It  is  as  clear  as  day  that  the  same  activity  in  the  nervous  sys- 
tem of  an  animal,  or  even  in  my  own  nervous  system,  observed  by 
myself,  first  by  means  of  physiological  methods  from  without,  and 
second,  as  reflecting  itself  in  my  consciousness,  must  appear  to  me 
to  be  totally  different,  and  it  would  indeed  be  labor  lost  to  try  to 
convert  the  physiological  into  psychological  qualities  or  vice  versa. 
We  cannot  even  convert  one  psychological  quality  into  another,  so 
far  as  the  reality  symbolised  by  both  is  concerned  ;  e.  g.,  the  tone, 


8  ANTS  AND  SOME   OTHER   INSECTS. 

the  visual  and  tactile  sensation,  which  a  uniform,  low,  tuning-fork 
vibration  produces  on  our  three  corresponding  senses.  Neverthe- 
less, we  may  infer  inductively  that  it  is  the  same  reality,  the  same 
vibration  which  is  symbolised  for  us  in  these  three  qualitatively 
and  totally  different  modes;  i.  e.,  produces  in  us  these  three  differ- 
ent psychical  impressions  which  cannot  be  transformed  into  one 
another.  These  impressions  depend  on  activities  in  different  parts 
of  the  brain  and  are,  of  course,  as  such  actually  different  from  one 
another  in  the  brain.  We  speak  of  psycho-physiological  identity 
only  when  we  mean,  on  the  one  hand,  the  cortical  neurocyme  which 
directly  conditions  the  conscious  phenomena  known  to  us,  on  the 
other  hand,  the  corresponding  phenomena  of  consciousness. 

And,  in  fact,  a  mind  conceived  as  dualistic  could  only  be  de- 
void of  energy  or  energy-containing.  If  it  be  conceived  as  devoid 
of  energy  (Wasmann),  i.  e.,  independent  of  the  laws  of  energy, 
we  have  arrived  at  a  belief  in  the  miraculous,  a  belief  which  coun- 
tenances the  interference  with  and  arbitrary  suspension  of  the  laws 
of  nature.  If  it  be  conceived  as  energy-containing,  one  is  merely 
playing  upon  words,  for  a  mind  which  obeys  the  law  of  energy  is 
only  a  portion  of  the  cerebral  activities  arbitrarily  severed  from  its 
connections  and  dubbed  "psychic  essence,"  only  that  this  may  be 
forthwith  discredited.  Energy  can  only  be  transformed  qualita- 
tively, not  quantitatively.  A  mind  conceived  as  dualistic,  if  sup- 
posed to  obey  the  law  of  energy,  would  have  to  be  transformed 
completely  into  some  other  form  of  energy.  But  then  it  would  no 
longer  be  dualistic,  i.  e.,  no  longer  essentially  different  from  the 
brain-activities. 

Bethe,  Uexkull,  and  others  would  require  us  to  hold  fast  to 
the  physiological  method,  because  it  alone  is  exact  and  restricts  it- 
self to  what  can  be  weighed  and  measured.  This,  too,  is  an  error 
which  has  been  refuted  from  time  immemorial.  Only  pure  mathe- 
matics is  exact,  because  in  its  operations  it  makes  use  solely  of 
equations  of  abstract  numbers.  The  concrete  natural  sciences  can 
never  be  exact  and  are  as  unable  to  subsist  without  the  inductive 
method  of  inference  from  analogy  as  a  tree  without  its  roots.  Bethe 
and  Uexkull  do  not  seem  to  know  that  knowledge  is  merely  rela- 


ANTS  AND  SOME  OTHER  INSECTS.  9 

live.  They  demand  absolute  exactitude  and  cannot  understand 
that  such  a  thing  is  impossible.  Besides,  physiology  has  no  reason 
to  pride  itself  upon  the  peculiar  exactitude  of  its  methods  and  re- 
sults. 

Although  we  know  that  our  whole  psychology  appears  as  the 
activity  of  our  cerebrum  in  connection  with  the  activities  of  more 
subordinate  nerve- centers,  the  senses  and  the  muscles,  nevertheless 
for  didactic  purposes  it  may  be  divided  into  the  psychology  of  cog- 
nition, of  feeling  and  volition.  Relatively  speaking,  this  subdivi- 
sion has  an  anatomico-physiological  basis.  Cognition  depends,  in 
the  first  instance,  on  the  elaboration  of  sense-impressions  by  the 
brain ;  the  will  represents  the  psycho-  or  cerebrofugal  resultants  of 
cognition  and  the  feelings  together  with  their  final  transmission  to 
the  muscles.  The  feelings  represent  general  conditions  of  excita- 
tion of  a  central  nature  united  with  elements  of  cognition  and  with 
cerebrofugal  impulses,  which  are  relatively  differentiated  and  re- 
fined by  the  former,  but  have  profound  hereditary  and  phylogenetic 
origins  and  are  relatively  independent.  There  is  a  continual  inter- 
action of  these  three  groups  of  brain-activities  upon  one  another. 
Sense-impressions  arouse  the  attention ;  this  necessitates  move- 
ments ;  the  latter  produce  new  sense-impressions  and  call  for  an 
active  selection  among  themselves.  Both  occasion  feelings  of  pleas- 
ure and  pain  and  these  again  call  forth  movements  of  defense, 
flight,  or  desire,  and  bring  about  fresh  sense-impressions,  etc. 
Anatomically,  at  least,  the  sensory  pathways  to  the  brain  and  their 
cortical  centers  are  sharply  separated  from  the  centers  belonging 
to  the  volitional  pathways  to  the  muscles.  Further  on  in  the  cere- 
brum, however,  all  three  regions  merge  together  in  many  neurons 
of  the  cortex. 

Within  ourselves,  moreover,  we  are  able  to  observe  in  the  three 
above-mentioned  regions  all  varieties  and  degrees  of  so-called 
psychic  dignity,  from  the  simplest  reflex  to  the  highest  mental 
manifestations.  The  feelings  and  impulses  connected  with  self- 
preservation  (hunger,  thirst,  fear)  and  with  reproduction  (sexual 
love  and  its  concomitants)  represent  within  us  the  region  of  long- 
inherited,  profoundly  phyletic,  fixed,  instinct-life.  These  instincts 


IO  ANTS  AND  SOME  OTHER   INSECTS. 

are  nevertheless  partially  modified  and  partly  kept  within  due 
bounds  through  the  interference  of  the  higher  cerebral  activities. 
The  enormous  mass  of  brain-substance,  which  in  man  stands  in  no 
direct  relation  to  the  senses  and  musculature,  admits  not  only  of 
an  enormous  storing  up  of  impressions  and  of  an  infinite  variety  of 
motor  innervations,  but  above  all,  of  prodigious  combinations  of 
these  energies  among  themselves  through  their  reciprocal  activities 
and  the  awakening  of  old,  so-called  memory  images  through  the 
agency  of  new  impressions.  In  contradistinction  to  the  compul- 
sory, regular  activities  of  the  profoundly  phyletic  automatisms,  I 
have  used  the  term  "plastic"  to  designate  those  combinations  and 
individual  adaptations  which  depend  on  actual  interaction  in  the 
activities  of  the  cerebrum.  Its  loftiest  and  finest  expression  is  the 
plastic  imagination,  both  in  the  province  of  cognition  and  in  the 
province  of  feeling,  or  in  both  combined.  In  the  province  of  the 
will  the  finest  plastic  adaptability,  wedded  to  perseverance  and 
firmness,  and  especially  when  united  with  the  imagination,  yields 
that  loftiest  mental  condition  which  gradually  brings  to  a  conclu- 
sion during  the  course  of  many  years  decisions  that  have  been  long 
and  carefully  planned  and  deeply  contemplated.  Hence  the  plas- 
tic gift  of  combination  peculiar  to  genius  ranks  much  higher  than 
any  simpler  plastic  adaptability. 

The  distinction  between  automatism  and  plasticity  in  brain- 
activity  is,  however,  only  a  relative  one  and  one  of  degree.  In  the 
most  different  instincts  which  we  are  able  to  influence  through  our 
cerebrum,  i.  e.,  more  or  less  voluntarily,  like  deglutition,  respira- 
tion, eating,  drinking,  the  sexual  impulse,  maternal  affection,  jeal- 
ousy, we  observe  gradations  between  compulsory  heredity  and  plas- 
tic adaptability,  yes,  even  great  individual  fluctuations  according 
to  the  intensity  of  the  corresponding  hereditary  predispositions. 

Now  it  is  indisputable  that  the  individual  Pithecanthropus  or 
allied  being,  whose  cerebrum  was  large  enough  gradually  to  con- 
struct from  onomatopceas,  interjections  and  the  like,  the  elements 
of  articulate  speech,  must  thereby  have  acquired  a  potent  means  of 
exploiting  his  brain.  Man  first  fully  acquired  this  power  through 
written  language.  Both  developed  the  abstract  concept  symbolised 


ANTS  AND  SOME  OTHER   INSECTS.  II 

by  words,  as  a  higher  stage  in  generalisation.  All  these  things 
give  man  a  colossal  advantage,  since  he  is  thereby  enabled  to  stand 
on  the  shoulders  of  the  written  encyclopaedia  of  his  predecessors. 
This  is  lacking  in  all  animals  living  at  the  present  time.  Hence,  if 
we  would  compare  the  human  mind  with  the  animal  mind,  we  must 
turn,  not  to  the  poet  or  the  savant,  but  to  the  Wedda  or  at  any  rate 
to  the  illiterate.  These  people,  like  children  and  animals,  are  very 
simple  and  extremely  concrete  in  their  thinking.  The  fact  that  it 
is  impossible  to  teach  a  chimpanzee  brain  the  symbols  of  language 
proves  only  that  it  is  not  sufficiently  developed  for  this  purpose. 
But  the  rudiments  are  present  nevertheless.  Of  course  the  "lan- 
guage" of  parrots  is  no  language,  since  it  symbolises  nothing.  On 
the  other  hand,  some  animals  possess  phyletic,  i.  e.,  hereditarily 
and  instinctively  fixed  cries  and  gesture,  which  are  as  instinctively 
understood.  Such  instinctive  animal  languages  are  also  very  widely 
distributed  and  highly  developed  among  insects,  and  have  been 
fixed  by  heredity  for  each  species.  Finally  it  is  possible  to  develop 
by  training  in  higher  animals  a  certain  mimetic  and  acoustic  conven- 
tional language-symbolism,  by  utilising  for  this  purpose  the  pecu- 
liar dispositions  of  such  species.  Thus  it  is  possible  to  teach  a 
dog  to  react  in  a  particular  manner  to  certain  sounds  or  signs,  but 
it  is  impossible  to  teach  a  fish  or  an  ant  these  things.  The  dog 
comprehends  the  sign,  not,  of  course,  with  the  reflections  of  human 
understanding,  but  with  the  capacity  of  a  dog's  brain.  And  it  is, 
to  be  sure,  even  more  impossible  to  teach  its  young  an  accomplish- 
ment so  lofty  for  its  own  brain  as  one  which  had  to  be  acquired  by 
training,  than  for  the  Wedda  or  even  the  negro  to  transmit  his  ac- 
quired culture  by  his  own  impulse.  Even  the  impulse  to  do  this  is 
entirely  lacking.  Nevertheless,  every  brain  that  is  trained  by  man 
is  capable  of  learning  and  profiting  much  from  the  experience  of 
its  own  individual  life.  And  one  discovers  on  closer  examination 
that  even  lower  animals  may  become  accustomed  to  some  extent  to 
one  thing  or  another,  and  hence  trained,  although  this  does  not 
amount  to  an  understanding  of  conventional  symbols. 

In  general  we  may  say,  therefore,  that  the  central  nervous  sys- 
"    tern  operates  in  two  ways  :  automatically  and  plastically. 


12  ANTS  AND   SOME  OTHER   INSECTS. 

The  so-called  reflexes  and  their  temporary,  purposefully  adap- 
tive, but  hereditarily  stereotyped  combinations,  which  respond 
always  more  or  less  in  the  same  manner  to  the  same  stimuli,  con- 
stitute the  paradigm  of  automatic  activities.  These  have  the  de- 
ceptive appearance  of  a  "machine"  owing  to  the  regularity  of  their 
operations.  But  a  machine  which  maintains,  constructs,  and  re- 
produces itself  is  not  a  machine.  In  order  to  build  such  a  machine 
we  should  have  to  possess  the  key  of  life,  i.  e.,  the  understanding 
of  the  supposed,  but  by  no  means  demonstrated,  mechanics  of  liv- 
ing protoplasm.  Everything  points  to  the  conclusion  that  the  in- 
stinctive automatisms  have  been  gradually  acquired  and  heredita- 
rily fixed  by  natural  selection  and  other  factors  of  inheritance.  But 
there  are  also  secondary  automatisms  or  habits  which  arise  through 
the  frequent  repetition  of  plastic  activities  and  are  therefore  espe- 
cially characteristic  of  man's  enormous  brain-development. 

In  all  the  psychic  provinces  of  intellect,  feeling,  and  will, 
habits  follow  the  constant  law  of  perfection  through  repetition. 
Through  practice  every  repeated  plastic  brain-activity  gradually 
becomes  automatic,  becomes  "second  nature,"  i.  e.,  similar  to  in- 
stinct. Nevertheless  instinct  is  not  inherited  habit,  but  phylogenet- 
ically  inherited  intelligence  which  has  gradually  become  adapted 
and  crystalised  by  natural  selection  or  by  some  other  means. 

Plastic  activity  manifests  itself,  in  general,  in  the  ability  of  the 
nervous  system  to  conform  or  adapt  itself  to  new  and  unexpected 
conditions  and  also  through  its  faculty  of  bringing  about  internally 
new  combinations  of  neurocyme.  Bethe  calls  this  the  power  of 
modification.  But  since,  notwithstanding  his  pretended  issue  with 
anthropomorphism,  he  himself  continually  proceeds  in  an  anthro- 
pomorphic spirit  and  demands  human  ratiocination  of  animals,  if 
they  are  to  be  credited  with  plasticity  (power  of  modification), — he 
naturally  overlooks  the  fact  that  the  beginnings  of  plasticity  are 
primordial,  that  they  are  in  fact  already  present  in  the  Amoeba, 
which  adapts  itself  to  its  environment.  Nor  is  this  fact  to  be  con- 
jured out  of  the  world  by  Loeb's  word  "tropisms." 

Automatic  and  plastic  activities,  whether  simple  or  complex, 
are  merely  relative  antitheses.  They  grade  over  into  each  other,  ' 


ANTS  AND  SOME  OTHER  INSECTS.  13 

e.  g.,  in  the  formation  of  habits  but  also  in  instincts.  In  their  ex- 
treme forms  they  resemble  two  terminal  branches  of  a  tree,  but 
they  may  lead  to  similar  results  through  so-called  convergence  of 
the  conditions  of  life  (slavery  and  cattle-keeping  among  ants  and 
men).  The  automatic  may  be  more  easily  derived  from  the  plastic 
activities  than  vice  versa.  One  thing  is  established,  however:  since 
a  tolerably  complicated  plastic  activity  admits  of  many  possibilities 
of  adaptation  in  the  individual  brain,  it  requires  much  more  nerv- 
ous substance,  many  more  neurons,  but  has  more  resistances  to 
overcome  in  order  to  attain  a  complicated  result.  The  activities 
of  an  Amoeba  belong  therefore  rather  to  the  plasticity  of  living 
molecules,  but  not  as  yet  to  that  of  cooperating  nerve-elements ;  as 
cell-plasticity  it  should  really  be -Designated  as  "undifferentiated."1 
There  are  formed  in  certain  animals  specially  complex  automatisms, 
or  instincts,  which  require  relatively  little  plasticity  and  few  neu- 
rons. In  others,  on  the  contrary,  there  remains  relatively  consider- 
able nerve-substance  for  individual  plasticity,  while  the  instincts 
are  less  complicated.  Other  animals,  again,  have  little  besides  the 
lower  reflex  centers  and  are  extremely  poor  in  both  kinds  of  com- 
plex activities.  Still  others,  finally,  are  rich  in  both.  Strong  so- 
called  "hereditary  predispositions"  or  unfinished  instincts  consti- 
tute the  phylogenetic  transitions  between  both  kinds  of  activity 
and  are  of  extraordinarily  high  development  in  man. 

Spoken  and  especially  written  language,  moreover,  enable  man 
to  exploit  his  brain  to  a  wonderful  extent.  This  leads  us  to  under- 
estimate animals.  Both  in  animals  and  man  the  true  value  of  the 
brain  is  falsified  by  training,  i.  e.,  artificially  heightened.  We 
overestimate  the  powers  of  the  educated  negro  and  the  trained  dog 
and  underestimate  the  powers  of  the  illiterate  individual  and  the 
wild  animal. 

I  beg  your  indulgence  for  this  lengthy  introduction  to  my  sub- 

1  If  I  expressly  refrain  from  accepting  the  premature  and  unjustifiable  identifi- 
cation of  cell-life  with  a  "machine,"  I  nevertheless  do  not  share  the  so-called  vital- 
istic  views.  It  is  quite  possible  that  science  may  sometime  be  able  to  produce  liv- 
ing protoplasm  from  inorganic  matter.  The  vital  forces  have  undoubtedly  origi- 
nated from  physico-chemical  forces.  But  the  ultimate  nature  of  the  latter  and  of 
the  assumed  material  atoms  is,  of  course,  metaphysical,  i.  e.,  unknowable. 


14  ANTS  AND  SOME  OTHER  INSECTS. 

ject,  but  it  seemed  necessary  that  we  should  come  to  some  under- 
standing concerning  the  validity  of  comparative  psychology.  My 
further  task  now  consists  in  demonstrating  to  you  what  manner  of 
psychical  faculties  may  be  detected  in  insects.  Of  course,  I  shall 
select  in  the  first  place  the  ants  as  the  insects  with  which  .1  am 
most  familiar.  Let  us  first  examine  the  brain  of  these  animals. 

In  order  to  determine  the  psychical  value  of  a  central  nervous 
system  it  is  necessary,  first,  to  eliminate  all  the  nerve-centers  which 
subserve  the  lower  functions,  above  the  immediate  innervation  of 
the  muscles  and  sense-organs  as  first  centers.  The  volume  of  such 
neuron-complexes  does  not  depend  on  the  intricacy  of  mental  work 
but  on  the  number  of  muscle-fibres  concerned  in  it,  the  sensory 
surfaces,  and  the  reflex  appara(prs,  hence  above  all  things  on  the 
size  of  the  animals.  Complex  instincts  already  require  the  inter- 
vention of  much  more  plastic  work  and  for  this  purpose  such  nerve- 
centers  alone  would  be  inadequate. 

A  beautiful  example  of  the  fact  that  complex  mental  combina- 
tions require  a  large  nerve-center  dominating  the  sensory  and  mus- 
cular centers  is  furnished  by  the  brain  of  the  ant.  The  ant-colony 
commonly  consists  of  three  kinds  of  individuals :  the  queen,  or 
female  (largest),  the  workers  which  are  smaller,  and  the  males 
which  are  usually  larger  than  the  workers.  The  workers  excel  in 
complex  instincts  and  in  clearly  demonstrable  mental  powers 
(memory,  plasticity,  etc.).  These  are  much  less  developed  in  the 
queens.  The  males  are  incredibly  stupid,  unable  to  distinguish 
friends  from  enemies  and  incapable  of  finding  their  wayjaack  to 
their  nest.  Nevertheless  the  latter  have  very  highly  developed 
eyes  and  antennae,  i.  e.,  the  two  sense-organs  which  alone  are  con- 
nected with  the  brain,  or  supra-oesophageal  ganglion  and  enable 
them  to  possess  themselves  of  the  females  during  the  nuptial  flight. 
No  muscles  are  innervated  by  the  supra-oesophageal  ganglion. 
These  conditions  greatly  facilitate  the  comparison  of  the  percep- 
tive organs,  i.  e.,  of  the  brain  (corpora  pedunculata)  in  the  three 
sexes.  This  is  very  large  in  the  worker,  much  smaller  in  the  fe- 
male, and  almost  vestigial  in  the  male,  whereas  the  optic  and 
olfactory  lobes  are  very  large  in  the  latter.  The  cortical  portion 


ANTS  AND   SOME  OTHER   INSECTS.  15 

of  the  large  worker  brain  is,  moreover,  extremely  rich  in  cellular 
elements.  In  this  connection  I  would  request  you  to  glance  at  the 
figures  and  their  explanation. 

Very  recently,  to  be  sure,  it  has  come  to  be  the  fashion  to  un- 
derestimate the  importance  of  brain-morphology  in  psychology  and 
even  in  nerve-physiology.  But  fashions,  especially  such  absurd 
ones  as  this,  should  have  no  influence  on  true  investigation.  Of 
course,  we  should  not  expect  anatomy  to  say  what  it  was  never  in- 
tended to  say. 

In  ants,  injury  to  the  cerebrum  leads  to  the  same  results  as  in- 
jury to  the  brain  of  the  pigeon. 

In  this  place  I  would  refer  you  for  a  fuller  account  of  the  de- 
tails of  sensation  and  the  psychiu  peculiarities  of  insects  to  my 
more  extended  work  above  mentioned  :  Sensations  des  Insectes. 

It  can  be  demonstrated  that  insects  possess  the  senses  of 
sight,  smell,  taste,  and  touch.  The  auditory  sense  is  doubtful. 
Perhaps  a  sense  of  touch  modified  for  the  perception  of  delicate 
vibrations  may  bear  a  deceptive  resemblance  to  hearing.  A  sixth 
sense  has  nowhere  been  shown  to  occur.  A  photodermatic  sense, 
modified  for  light-sensation,  must  be  regarded  as  a  form  of  the  tac- 
tile sense.  It  occurs  in  many  insects.  This  sense  is  in  no  respect 
of  an  optic  nature.  In  aquatic  insects  the  olfactory  and  gustatory 
senses  perhaps  grade  over  into  each  other  somewhat  (Nagel),  since 
both  perceive  chemical  substances  dissolved  in  the  water. 

The  visual  sense  of  the  facetted  eyes  is  especially  adapted  for 
seeing  movements,  i.  e. ,  for  perceiving  relative  changes  of  position 
in  the  retinal  image.  In  flight,  it  is  able  to  localise  large  spatial 
areas  admirably,  but  must  show  less  definite  contours  of  the  ob- 
jects than  our  eyes.  The  compound  eye  yields  only  a  single  up- 
right image  (Exner),  the  clearness  of  which  increases  with  the 
number  of  facets  and  the  convexity  of  the  eye.  Exner  succeeded 
in  photographing  this  image  in  the  fire-fly  (Lampyris).  As  the 
eyes  are  immovable  the  sight  of  resting  objects  soon  disappears  so 
far  as  the  resting  insect  is  concerned.  For  this  reason  resting  in- 
sects are  easily  captured  when  very  slowly  approached.  In  flight 
insects  orient  themselves  in  space  by  means  of  their  compound 


Fig.  W. 


Fig.  F. 


Fig.  M. 


EXPLANATION  OF  THE  FIGURES. 

Brain  (supra-cesophageal  ganglion)  of  an  ant  (Lasius fuliginosus),  magnified 
60  diameters,  seen  from  above. 

Fig.  W.  Brain  of  the  Worker. 

Fig.  F.    Brain  of  the  Queen  (Female) 

Fig.  M.  Brain  of  the  Male. 

St.  =  Brain  trunk.  L.  op.  =Lobus  opticus  (optic  lobe).  L.  olf.  =  Lobus  olfac- 
torius  sive  antennalis  (olfactory  lobe).  N.  =  Facetted  eye.  N.  olf.  =Nervus  olfac- 
torius  sive  antennalis  (olfactory  nerve).  O.  =Ocelli,  or  simple  eyes  with  their 
nerves  (present  only  in  the  male  and  queen).  H.  =  Cellular  brain  cortex  (developed 
only  in  the  worker  and  queen).  C.  p.  =  Corpora  pedunculata,  or  fungiform  bodies 
(developed  only  in  the  worker  and  queen).  Jf.  =Rudimental  cortex  of  male. 

The  length  of  the  whole  ant  is  : 

in  the  worker  4.5  mm  ; 
in  the  queen  6.0  mm  ; 
in  the  male  4.5  mm. 

N.  B.  The  striation  of  the  corpora  pedunculata  and  their  stems  is  represented 
diagrammatically,  for  the  purpose  of  indicating  rather  coarsely  their  extremely 
delicate  fibrillar  structure. 


l6  ANTS  AND   SOME  OTHER  INSECTS. 

eyes.  Odor,  when  perceived,  merely  draws  these  animals  in  a 
particular  direction.  When  the  compound  eyes  are  covered,  all 
powers  of  orientation  in  the  air  are  lost.  Many  insects  can  adapt 
their  eyes  for  the  day  or  night  by  a  shifting  of  the  pigment.  Ants 
see  the  ultra-violet  with  their  eyes.  Honey-bees  and  humble-bees 
can  distinguish  colors,  but  obviously  in  other  tones  than  we  do, 
since  they  cannot  be  deceived  by  artificial  flowers  of  the  most  skil- 
ful workmanship.  This  may  be  due  to  admixtures  of  the  ultra-violet 
rays  which  are  invisible  to  our  eyes. 

The  ocelli  (simple  eyes)  play  a  subordinate  role,  and  probably 
serve  as  organs  of  sight  for  objects  situated  in  the  immediate  vicin- 
ity and  in  dark  cavities. 

The  olfactory  sense  has  its  seat  in  the  antennae,  usually  in  the 
club-shaped  flagellum,  or  rather  in  the  pore-plates  and  olfactory 
rods  of  these  portions  of  the  antennae.  On  account  of  its  external 
and  moveable  position  at  the  tip  of  the  antenna,  the  olfactory  or- 
gan possesses  two  properties  which  are  lacking  in  the  vertebrates, 
and  particularly  in  man.  These  are  : 

1.  The  power  of  perceiving  the  chemical  nature  of  a  body  by 
direct  contact  (contact-odor); 

2.  The  power  of  space-perception  and  of  perceiving  the  form 
of  objects  and  that  of  the  animal's  own  trail  by  means  of  odor,  and 
the  additional  property  of  leaving  associated  memories. 

The  olfactory  sense  of  insects,  therefore,  gives  these  animals 
definite  and  clear-cut  perceptions  of  space-relations,  and  enables 
the  animal  while  moving  on  the  surface  of  the  ground  to  orient  it- 
self with  facility.  I  have  designated  this  sense,  which  is  thus  quali- 
tatively, i.  e.,  in  its  specific  energy,  very  different  from  our  olfac- 
tory sense,  as  the  topochemical  (olfactory)  sense.  Probably  the 
pore-plates  are  used  for  perceiving  odor  at  a  distance  and  the  olfac- 
tory rods  for  contact-odor,  but  this  is  pure  conjecture.  Extirpation 
of  the  antennae  destroys  the  power  of  distinguishing  friends  from 
enemies  and  deprives  the  ant  of  the  faculty  of  orienting  itself  on 
the  ground  and  of  finding  its  way,  whereas  it  is  possible  to  cut  off 
three  legs  and  an  antenna  without  seriously  impairing  these  powers. 
The  topochemical  sense  always  permits  the  ant  to  distinguish  be- 


ANTS  AND  SOME  OTHER   INSECTS.  IJ 

tween  the  directions  of  its  trail,  a  faculty  which  Bethe  attributes  to 
a  mysterious  polarisation.  The  ability  to  sense  different  odors 
varies  enormously  in  different  insects.  An  object  possessing  odor 
for  one  species  is  often  odorless  for  other  species  (and  for  ourselves) 
and  vice  versa. 

The  gustatory  organs  are  situated  on  the  mouth-parts.  Among 
insects  the  reactions  of  this  sense  are  very  similar  to  our  own.  Will 
accustomed  some  wasps  to  look  in  a  particular  place  for  honey, 
which  he  afterwards  mixed  with  quinine.  The  wasps  detected  the 
substance  at  once,  made  gestures  of  disgust,  and  never  returned  to 
the  honey.  Mixing  the  honey  with  alum  had  the  same  result.  At 
first  they  returned,  but  after  the  disagreeable  gustatory  experience 
they  failed  to  reappear.  Incidentally  this  is  also  a  proof  of  their 
gustatory  memory  and  of  their  powers  of  association. 

Several  organs  have  been  found  and  described  as  auditory. 
But  after  their  removal  the  supposed  reaction  to  sounds  persists. 
This  would  seem  to  indicate  that  a  deceptive  resemblance  to  hear- 
ing may  be  produced  by  the  perception  of  delicate  vibrations 
through  the  tactile  sense  (Duges). 

The  tactile  sense  is  everywhere  represented  by  tactile  hairs 
and  papillae.  It  reacts  more  especially  to  delicate  tremors  of  the 
atmosphere  or  soil.  Certain  arthropods,  especially  the  spiders, 
orient  themselves  mainly  by  means  of  this  sense. 

It  may  be  demonstrated  that  insects,  according  to  the  species 
and  conditions  of  life,  use  their  different  senses  in  combination  for 
purposes  of  orienting  themselves  and  for  perceiving  the  external 
world.  Many  species  lack  eyes  and  hence  also  the  sense  of  sight. 
In  others,  again,  the  olfactory  sense  is  obtuse  ;  certain  other  forms 
lack  the  contact-odor  sense  (e.  g.,  most  Diptera). 

It  has  been  shown  that  the  superb  powers  of  orientation  ex- 
hibited by  certain  aerial  animals,  like  birds  (carrier-pigeons),  bees, 
etc.,  depend  on  vision  and  its  memories.  Movement  in  the  air 
gives  this  sense  enormous  and  manifold  values.  The  semi-circular 
canals  of  the  auditory  organ  are  an  apparatus  of  equilibrium  in 
vertebrates  and  mediate  sensations  of  acceleration  and  rotation 
(Mach-Breuer),  but  do  not  give  external  orientation.  For  the  dem- 


j8  ANTS  AND  SOME  OTHER  INSECTS. 

onstration  of  these  matters  I  must  refer  you  to  my  work  above- 
cited.  A  specific,  magnetic,  or  other  mode  of  orientation,  indepen- 
dent of  the  known  senses,  does  not  exist. 

The  facts  above  presented  constitute  the  basis  of  insect  psy- 
chology. The  social  insects  are  especially  favorable  objects  for 
study  on  account  of  their  manifold  reciprocal  relationships.  If  in 
speaking  of  their  behavior  I  use  terms  borrowed  from  human  life, 
I  request  you,  once  for  all,  to  bear  in  mind  that  these  are  not  to 
be  interpreted  in  an  anthropomorphic  but  in  an  analogous  sense. 

THE  PROVINCE  OF  COGNITION. 

Many  insects  (perhaps  all,  in  a  more  rudimental  condition) 
possess  memory,  i.  e.,  they  are  able  to  store  up  sense-impressions 
in  their  brains  for  subsequent  use.  Insects  are  not  merely  attracted 
directly  by  sensory  stimuli,  as  Bethe  imagines.  Huber,  myself, 
Fabre,  Lubbock,  Wasmann,  Von  Buttel-Reepen,  have  demonstrated 
this  fact  experimentally.  That  bees,  wasps,  etc.,  can  find  their  way 
in  flight  through  the  air,  notwithstanding  wind  and  rain  (and  hence 
under  circumstances  precluding  the  existence  of  any  possible  odor- 
iferous trail),  and  even  after  the  antennae  have  been  cut  off,  to  a 
concealed  place  where  they  have  found  what  they  desired,  though 
this  place  may  be  quite  invisible  from  their  nest,  and  this  even 
after  the  expiration  of  days  and  weeks,  is  a  fact  of  special  impor- 
tance as  proof  of  the  above  assertion.  It  can  be  shown  that  these 
insects  recognise  objects  by  means  of  their  colors,  their  forms,  and 
especially  by  their  position  in  space.  Position  they  perceive 
through  the  mutual  relations  and  succession  of  the  large  objects  in 
space,  as  these  are  revealed  to  them  in  their  rapid  change  of  place 
during  flight  in  their  compound  eyes  (shifting  of  retinal  images). 
Especially  the  experiments  performed  by  Von  Buttel-Reepen  and 
myself  leave  no  doubt  concerning  this  fact.  Additional  proof  of  a 
different  nature  is  furnished  by  Von  Buttel,  who  found  that  ether  or 
chloroform  narcosis  deprives  bees  of  all  memory.  By  this  means 
enemies  can  be  converted  into  friends.  Under  these  circumstances, 
too,  all  memory  of  locality  is  lost  and  must  be  reacquired  by  means 


ANTS  AND  SOME  OTHER  INSECTS.  ig 

of  a  new  flight  of  orientation.  An  animal,  however,  certainly  can- 
not forget  without  having  remembered. 

The  topochemical  antennal  sense  also  furnishes  splendid  proofs 
of  memory  in  ants,  bees,  etc.  An  ant  may  perform  an  arduous 
journey  of  thirty  meters  from  her  ruined  nest,  there  find  a  place 
suitable  for  building  another  nest,  return,  orienting  herself  by 
means  of  her  antennae,  seize  a  companion  who  forthwith  rolls  her- 
self about  her  abductrix,  and  is  carried  to  the  newly  selected  spot. 
The  latter  then  also  finds  her  way  to  the  original  nest,  and  both 
each  carry  back  another  companion,  etc.  The  memory  of  the  suit- 
able nature  of  the  locality  for  establishing  a  new  nest  must  exist  in 
the  brain  of  the  first  ant  or  she  would  not  return,  laden  with  a  com- 
panion, to  this  very  spot.  The  slave-making  ants  (Polyergus}  un- 
dertake predatory  expeditions,  led  by  a  few  workers,  who  for  days 
and  weeks  previously  have  been  searching  the  neighborhood  for 
nests  of  Formica  fusca.  The  ants  often  lose  their  way,  remain 
standing  and  hunt  about  for  a  long  time  till  one  or  the  other  finds 
the  topochemical  trail  and  indicates  to  the  others  the  direction  to 
be  followed  by  rapidly  pushing  ahead.  Then  the  pupae  of  the  For- 
mica fusca  nest,  which  they  have  found,  are  brought  up  from  the 
depths  of  the  galleries,  appropriated  and  dragged  home,  often  a 
distance  of  forty  meters  or  more.  If  the  plundered  nest  still  con- 
tains pupae,  the  robbers  return  on  the  same  or  following  days  and 
carry  off  the  remainder,  but  if  there  are  no  pupae  left  they  do  not 
return.  How  do  the  Polyergus  know  whether  there  are  pupae  re- 
maining? It  can  be  demonstrated  that  smell  could  not  attract  them 
from  such  a  distance,  and  this  is  even  less  possible  for  sight  or  any 
other  sense.  Memory  alone,  i.  e.,  the  recollection  that  many  pupae 
still  remain  behind  in  the  plundered  nest  can  induce  them  to  re- 
turn. I  have  carefully  followed  a  great  number  of  these  predatory 
expeditions. 

While  Formica  species  follow  their  topochemical  trail  with 
great  difficulty  over  new  roads,  they  nevertheless  know  the  imme- 
diate surroundings  of  their  nest  so  well  that  even  shovelling  away 
the  earth  can  scarcely  disconcert  them,  and  they  find  their  way  at 
once,  as  Wasmann  emphatically  states  and  as  I  myself  have  often 


20  ANTS  AND   SOME  OTHER   INSECTS. 

observed.  That  this  cannot  be  due  to  smelling  at  long  range  can 
be  demonstrated  in  another  manner,  for  the  olfactory  powers  of  the 
genus  Formica,  like  those  of  honey-bees,  are  not  sufficiently  acute 
for  this  purpose,  as  has  been  shown  in  innumerable  experiments  by 
all  connoisseurs  of  these  animals.  Certain  ants  can  recognise  friends 
even  after  the  expiration  of  months.  In  ants  and  bees  there  are 
very  complex  combinations  and  mixtures  of  odors,  which  Von  But- 
tel  has  very  aptly  distinguished  as  nest-odor,  colony-  (family-)  odor, 
and  individual  odor.  In  ants  we  have  in  addition  a  species-odor, 
while  the  queen-odor  does  not  play  the  same  role  as  among  bees. 

It  follows  from  these  and  many  other  considerations  that  the 
social  Hymenoptera  can  store  up  in  their  brains  visual  images  and 
topochemical  odor-images  and  combine  these  to  form  perceptions 
or  something  of  a  similar  nature,  and  that  they  can  associate  such 
perceptions,  even  those  of  different  senses,  especially  sight,  odor, 
and  taste,  with  one  another  and  thereby  acquire  spatial  images. 

Huber  as  well  as  Von  Buttel,  Wasmann,  and  myself  have 
always  found  that  these  animals,  through  frequent  repetition  of  an 
activity,  journey,  etc.,  gain  in  the  certainty  and  rapidity  of  the  ex- 
ecution of  their  instincts.  Hence  they  form,  very  rapidly  to  be 
sure,  habits.  Von  Buttel  gives  splendid  examples  of  these  in  the 
robber-bees,  i.  e.,  in  some  of  the  common  honey-bees  that  have 
acquired  the  habit  of  stealing  the  honey  from  the  hives  of  strangers. 
At  first  the  robbers  display  some  hesitation,  though  later  they  be- 
come more  and  more  impudent.  But  he  who  uses  the  term  habit, 
must  imply  secondary  automatism  and  a  pre-existing  plastic  adapt- 
ability. Von  Buttel  adduces  an  admirable  proof  of  this  whole  mat- 
ter and  at  the  same,  time  one  of  the  clearest  and  simplest  refuta- 
tions of  Bethe's  innumerable  blunders,  when  he  shows  that  bees 
that  have  never  flown  from  the  hive,  even  though  they  may  be 
older  than  others  that  have  already  flown,  are  unable  to  find  their 
way  back  even  from  a  distance  of  a  few  meters,  when  they  are  un- 
able to  see  the  hive,  whereas  old  bees  know  the  whole  environ- 
ment, often  to  a  distance  of  six  or  seven  kilometers. 

It  results,  therefore,  from  the  unanimous  observations  of  all 
the  connoisseurs  that  sensation,  perception,  and  association,  infer- 


ANTS  AND  SOME  OTHER  INSECTS.  21 

ence,  memory  and  habit  follow  in  the  social  insects  on  the  whole 
the  same  fundamental  laws  as  in  the  vertebrates  and  ourselves. 
Furthermore,  attention  is  surprisingly  developed  in  insects,  often 
taking  on  an  obsessional  character  and  being  difficult  to  divert. 

On  the  other  hand,  inherited  automatism  exhibits  a  colossal 
preponderance.  The  above-mentioned  faculties  are  manifested 
only  in  an  extremely  feeble  form  beyond  the  confines  of  the  in- 
stinct-automatism stereotyped  in  the  species. 

An  insect  is  extraordinarily  stupid  and  inadaptable  to  all  things 
not  related  to  its  instincts.  Nevertheless  I  succeeded  in  teaching 
a  water-beetle  (Dytiscus  marginalis)  which  in  nature  feeds  only  in 
the  water,  to  eat  on  my  table.  While  thus  feeding,  it  always  exe- 
cuted a  clumsy  flexor-movement  with  its  fore-legs  which  brought  it 
over  on  its  back.  The  insect  learned  to  keep  on  feeding  while  on 
its  back,  but  it  would  not  dispense  with  this  movement,  which  is 
adapted  to  feeding  in  the  water.  On  the  other  hand,  it  always  at- 
tempted to  leap  out  of  the  water  (no  longer  fleeing  to  the  bottom 
of  the  vessel)  when  I  entered  the  room,  and  nU^>led  at  the  tip  of 
my  finger  in  the  most  familiar  manner.  Now  these  are  certainly 
plastic  variations  of  instinct.  In  a  simiter  manner  some  large 
Algerian  ants  which  I  transplanted  to  Zurich,  learned  during  the 
course  of  the  summer  months  to  close  the  entrance  of  their  nest 
with  pellets  of  earth,  because  they  were  being  persecuted  and  an- 
noyed by  our  little  Lasius  niger.  In  Algiers  I  always  saw  the  nest- 
opening  wide  open.  There  are  many  similar  examples  which  go 
to  show  that  these  tiny  animals  can  utilise  some  few  of  their  expe- 
riences even  when  this  requires  a  departure  from  the  usual  in- 
stincts. 

That  ants,  bees,  and  wasps  are  able  to  exchange  communica- 
tions that  are  understood,  and  that  they  do  not  merely  titillate  one 
another  with  their  antennae  as  Bethe  maintains,  has  been  demon- 
strated in  so  many  hundred  instances,  that  it  is  unnecessary  to 
waste  many  words  on  this  subject.  The  observations  of  a  single 
predatory  expedition  of  Polyergus,  with  a  standing  still  of  the  whole 
army  and  a  seeking  for  the  lost  trail,  is  proof  sufficient  of  the  above 
statement.  But,  of  course,  this  is  not  language  in  the  human  sense  ! 


22  ANTS  AND  SOME  OTHER   INSECTS. 

There  are  no  abstract  concepts  corresponding  to  the  signs.  We 
are  here  concerned  only  with  hereditary,  instinctively  automatic 
signs.  The  same  is  true  of  their  comprehension  (pushing  with  the 
head,  rushing  at  one  another  with  wide-open  mandibles,  titillation 
with  the  antennae,  stridulatory  movement  of  the  abdomen,  etc.). 
Moreover,  imitation  plays  a  great  role.  Ants,  bees,  etc.,  imitate 
and  follow  their  companions.  Hence  it  is  decidedly  erroneous  (and 
in  this  matter  Wasmann,  Von  Buttel,  and  myself  are  of  but  one 
opinion)  to  inject  human  thought-conception  and  human  ratiocina- 
tion into  this  instinct-language,  as  has  been  done  to  some  extent, 
at  least,  even  by  Pierre  Huber,  not  to  mention  others.  It  is  even 
very  doubtful  whether  a  so-called  general  sensory  idea  (i.  e.,  a  gen- 
eral idea  of  an  object,  like  the  idea  "ant,"  "enemy,"  "nest," 
"pupa")  can  arise  in  the  emmet  brain.  This  is  hardly  capable  of 
demonstration.  Undoubtedly  perception  and  association  can  be 
carried  on  in  a  very  simple  way,  after  the  manner  of  insects,  with- 
out ever  rising  to  such  complex  results.  At  any  rate  proofs  of  such 
an  assumption  are  lacking.  But  what  exists  is  surely  in  itself  suffi- 
ciently interesting  and  important.  It  gives  us  at  least  an  insight 
into  the  brain-life  of  these  animals. 

Better  than  any  generalisations,  a  good  example  will  show 
what  I  mean. 

Plateau  had  maintained  that  when  Dahlia  blossoms  are  covered 
with  green  leaves,  bees  nevertheless  return  to  them  at  once.  At 
first  he  concealed  his  Dahlias  incompletely  (i.  e.,  only  their  ray- 
florets),  afterwards  completely,  but  still  in  an  unsatisfactory  man- 
ner, and  inferred  from  the  results  that  bees  are  attracted  by  odor 
and  not  by  sight. 

a.  In  a  Dahlia  bed  visited  by  many  bees  and  comprising  about 
forty-three  floral  heads  of  different  colors,  I  covered  first  seventeen 
and  then  eight  at  2.15  P.  M.,  September  loth,  with  grape-leaves 
bent  around  them  and  fastened  with  pins. 

b.  Of  four  I  covered  only  the  yellow  disc ; 

c.  Of  one,  on  the  other  hand,  I  covered  only  the  outer  ray- 
florets,  leaving  the  disc  visible. 


ANTS  AND  SOME  OTHER  INSECTS.  23 

So  many  bees  were  visiting  the  Dahlias  that  at  times  there 
were  two  or  three  to  a  flower. 

Result :  Immediately  all  the  completely  covered  flowers  ceased 
to  be  visited  by  the  bees.  Dahlia  (<r)  continued  to  be  visited  like 
those  completely  visible.  The  bees  often  flew  to  Dahlias  (£)  but  at 
once  abandoned  them  ;  a  few,  however,  succeeded  in  finding  the 
disc  beneath  the  leaves. 

Then  as  soon  as  I  removed  the  covering  from  a  red  Dahlia  the 
bees  at  once  flew  to  it ;  and  soon  a  poorly  concealed  specimen  was 
detected  and  visited.  Later  an  inquisitive  bee  discovered  the  en- 
trance to  a  covered  Dahlia  from  the  side  or  from  below.  Thence- 
forth this  bee,  but  only  this  one,  returned  to  this  same  covered 
flower. 

Nevertheless  several  bees  seemed  to  be  seeking  the  Dahlias 
which  had  so  suddenly  disappeared.  Towards  5.30  o'clock  some 
of  them  had  detected  the  covered  flowers.  Thenceforth  these  in- 
sects were  rapidly  imitated  by  the  other  bees,  and  in  a  short  time 
the  hidden  flowers  were  again  being  visited.  As  soon  as  a  bee  had 
discovered  my  imposition  and  found  the  entrance  to  a  hidden 
flower,  she  flew  in  her  subsequent  journeys,  without  hesitation  to 
the  concealed  opening  of  the  grape-leaf.  As  long  as  a  bee  had 
merely  made  the  discovery  by  herself,  she  remained  unnoticed  by 
the  others.  When  this  was  accomplished  by  several,  however,  (usu- 
ally by  four  or  five,)  the  others  followed  their  example. 

Plateau,  therefore,  conducted  his  experiments  in  a  faulty  man- 
ner and  obtained  erroneous  results.  The  bees  still  saw  the  Dahlias 
which  he  at  first  incompletely  concealed.  Then,  by  the  time  he 
had  covered  them  up  completely,  but  only  from  above,  they  had 
already  detected  the  fraud  and  saw  the  Dahlias  also  from  the  side. 
Plateau  had  failed  to  take  into  consideration  the  bee's  memory  and 
attention. 

September  i3th  I  made  some  crude  imitations  of  Dahlias  by 
sticking  the  yellow  heads  of  Hieracium  (hawkweed)  each  in  a  Pe- 
tunia flower,  and  placed  them  among  the  Dahlias.  Neither  the 
Petunias  nor  the  Hieracium  had  been  visited  by  the  bees.  Never- 
theless many  of  the  honey  and  humble-bees  flew  at  first  to  the  arte- 


24  ANTS  AND  SOME  OTHER  INSECTS. 

facts  in  almost  as  great  numbers  as  to  the  Dahlias,  but  at  once 
abandoned  the  flowers  when  they  had  detected  the  error,  obviously 
by  means  of  their  sense  of  smell.  The  same  results  were  produced 
by  a  Dahlia,  the  disc  of  which  had  been  replaced  by  the  disc  of  a 
Hieracium. 

As  a  control  experiment  I  had  placed  a  beautiful,  odorous 
Dahlia  disc  among  the  white  and  yellow  Chrysanthemums  which 
had  been  neglected  by  the  bees.  For  a  whole  half  hour  the  bees 
flew  by  only  a  few  centimeters  above  the  disc  without  noticing  it ; 
not  till  then  was  it  visited  by  a  bee  that  happened  to  be  followed 
by  a  second.  From  this  moment  the  Dahlia  disc  which  lay  in  the 
path  of  flight  was  visited  like  the  others,  whereas  on  the  other  hand 
the  Petunia-Hieracium  artefacts,  now  known  to  be  fraudulent,  were 
no  longer  noticed. 

Plateau  has  demonstrated  that  artificial  flowers,  no  matter  how 
carefully  copied  from  the  human  standpoint,  are  not  noticed  by  in- 
sects. I  placed  artefacts  of  this  description  among  the  Dahlias. 
They  remained  in  fact  entirely  neglected.  Perhaps,  as  above  sug- 
gested, the  bees  are  able  to  distinguish  the  chlorophyll  colors  from 
other  artificial  hues,  owing  to  admixtures  of  the  ultra-violet  rays, 
or  by  some  other  means.  But  since  Plateau  imagines  that  the  arti- 
ficial flowers  repel  insects,  I  cut  out,  Sept.  igth,  the  following 
rather  crude  paper-flowers  : 

a.   A  red  flower ; 

ft.   A  white  flower  ; 

y.   A  blue  flower  ; 

8    A  blue  flower,  with  a  yellow  center  made  from  a  dead  leaf; 

e.   A  rose-colored  piece  of  paper  with  a  dry  Dahlia  disc; 

£.   A  green  Dahlia  leaf  (unchanged). 

It  was  nine  o'clock  in  the  morning.  I  placed  a  drop  of  honey 
on  each  of  the  six  artefacts  mounted  among  the  Dahlias.  For  a 
quarter  of  an  hour  many  bees  flew  past,  very  close  to  my  artefacts 
but  without  perceiving  and  hence  without  smelling  the  honey.  I 
went  away  for  an  hour.  On  my  return  artefact  8  was  without  honey, 
and  must  therefore  have  been  discovered  by  the  bees.  All  the 
others  had  remained  quite  untouched  and  unnoticed. 


ANTS  AND  SOME  OTHER  INSECTS.  25 

With  some  difficulty  I  next  undertook  to  bring  artefact  a  very 
close  to  a  bee  resting  on  a  Dahlia.  But  the  attention  of  the  bee 
was  so  deeply  engrossed  by  the  Dahlia  that  I  had  to  repeat  the  ex- 
periment four  or  five  times  till  I  succeeded  in  bringing  the  honey 
within  reach  of  her  proboscis.  The  insect  at  once  began  to  suck 
up  the  honey  from  the  paper-flower.  I  marked  the  bee's  back  with 
blue  paint  so  that  I  might  be  able  to  recognise  her,  and  repeated 
the  experiment  with  ft  and  c.  In  these  cases  one  of  the  bees  was 
painted  yellow,  the  other  white. 

Soon  the  blue  bee,  which  had  in  the  meantime  gone  to  the 
hive,  returned,  flew  at  once  to  a,  first  hovering  about  it  dubiously, 
then  to  8,  where  she  fed,  then  again  to  a,  but  not  to  the  Dahlias. 
Later  the  yellow  bee  returned  to  ft  and  fed,  and  flew  to  a  and  8 
where  she  again  fed,  but  gave  as  little  heed  to  the  Dahlias  as  did 
the  blue  bee. 

Thereupon  the  white  bee  returned  seeking  c,  but  failing  to  find 
it,  at  once  went  to  feeding  on  some  of  the  Dahlias.  But  she  tarried 
only  a  moment  on  each  Dahlia  as  if  tortured  by  the  idte  fi xe  of 
honey.  She  returned  to  the  artefacts,  the  perception  of  which, 
however,  she  was  not  quite  able  to  associate  with  the  memory  of 
the  honey  flavor.  At  last  she  found  a  separate  piece  of  e,  which 
happened  to  be  turned  down  somewhat  behind,  and  began  lapping 
up  the  honey. 

Thenceforth  the  three  painted  bees,  and  these  alone,  returned 
regularly  to  the  artefacts  and  no  longer  visited  the  Dahlias.  The 
fact  is  of  great  importance  that  the  painted  bees  entirely  of  their 
own  accord,  undoubtedly  through  an  instinctive  inference  from 
analogy,  discovered  the  other  artefacts  as  soon  as  their  attention 
had  been  attracted  by  the  honey  on  one  of  them,  notwithstanding 
the  fact  that  the  artefacts  were  some  distance  from  one  another  and 
of  different  colors.  For  were  not  the  Dahlias,  too,  which  they  had 
previously  visited,  of  different  colors?  Thus  the  blue  bee  flew  to 
a,  ft,  y,  and  8,  the  yellow  to  ft,  a,  8,  and  y,  the  white  e,  a,  ft,  and  8. 
Matters  continued  thus  for  half  an  hour.  The  hidden  green  £  was 
not  found,  evidently  because  it  was  indistinguishable  from  the  green 
foliage. 


26  ANTS  AND  SOME  OTHER   INSECTS. 

Finally  one  bee,  by  herself,  having  had  in  all  probability  her 
attention  attracted  by  the  three  others,  came  to  8  and  fed.  I  marked 
her  with  carmine.  Thereupon  she  flew  to  a  and  drove  the  blue  bee 
away.  Another  bee  was  attracted  to  e  of  her  own  accord  and  was 
painted  with  cinnobar.  Still  another  bee  came  by  herself  to  ft  and 
was  painted  green.  It  was  now  12.30  o'clock.  The  experiment 
had  therefore  lasted  more  than  three  hours,  and  during  this  time 
only  six  bees  had  come  to  know  the  artefacts,  while  the  great  ma- 
jority still  kept  on  visiting  the  Dahlias.  But  now  the  other  bees 
began  to  have  their  attention  attracted  by  the  visitors  to  the  arte- 
facts. One,  then  two,  then  three,  and  finally  more  new  ones  fol- 
lowed, and  I  had  not  sufficient  colors  with  which  to  mark  them. 
Every  moment  I  was  obliged  to  replenish  the  honey.  Then  I  went 
to  dinner  and  returned  at  1.25.  At  this  moment  seven  bees  were 
feeding  on  ft,  two  on  a,  one  on  y,  three  on  8,  the  white  one  alone 
on  e.  More  than  half  of  all  these  were  new,  unpainted  followers. 
Now  a  veritable  swarm  of  bees  threw  themselves  on  the  artefacts 
and  licked  up  the  last  traces  of  the  honey.  Then  for  the  first  time, 
after  more  than  four  hours,  a  bee  from  the  swarm  discovered  the 
honey  on  the  artefact  £,  which  on  account  of  its  .color  had  remained 
concealed  up  to  this  time  ! 

As  a  pack  of  hounds  throws  itself  on  an  empty  skeleton,  the 
swarm  of  bees,  now  completely  diverted  from  the  Dahlias,  cast 
themselves  on  the  completely  empty  artefacts  and  vainly  searched 
every  corner  of  them  for  honey.  It  was  1.55  P.  M.  The  bees  be- 
gan to  scatter  and  return  to  the  Dahlias.  Then  I  replaced  a  and 
ft  by  a  red  and  white  paper  respectively,  which  had  never  come  in 
contact  with  honey  and  could  not  therefore  smell  of  the  substance. 
These  pieces  of  paper,  nevertheless,  were  visited  and  examined  by 
various  bees,  whose  brains  were  still  possessed  with  the  fixed  idea 
of  the  flavor  of  honey.  The  white  bee,  e.  g.,  investigated  the  white 
paper  very  carefully  for  a  period  of  three  to  four  minutes.  There 
could,  of  course,  be  no  such  thing  as  an  unknown  force  or  attrac- 
tion of  odor,  or  brilliancy  of  floral  colors.  This  fact  can  only  be 
explained  by  an  association  of  space,  form,  and  color  memories  with 
memories  of  taste. 


ANTS  AND  SOME  OTHER  INSECTS.  27 

Thereupon  I  took  all  the  artefacts  in  my  left  hand  for  the  pur- 
pose of  carrying  them  away.  Two  or  three  bees  followed  me,  hov- 
ering about  my  left  hand,  and  tried  to  alight  on  the  empty  artefacts. 
The  space-image  had  changed  and  only  the  color  and  form  could 
any  longer  be  of  service  to  the  bees  in  their  recognition  of  these 
objects. 

This  experiment  is  so  clear  and  unequivocal  that  I  mention  it 
here  among  many  others.  It  demonstrates  : 

1.  The  space,  form,  and  color  perceptions  of  the  honey-bee. 
That  these  are  possible  only  through  the  agency  of  the  compound 
eyes  is  proved  by  other  experiments  (varnishing  the  eyes,  extirpa- 
tion of  the  antennae,  mouth-parts,  etc.). 

2.  The  memory  of  the  honey-bee,  in  particular  her  visual  and 
gustatory  memory. 

3.  Her  power  of  associating  gustatory  with  visual  memories. 

4.  Her  ability  instinctively  to  draw  inferences  from  analogy : 
If  she  has  once  been  offered  honey  in  an  artefact,  she  will  investi- 
gate others,  even  those  of  a  different  color  and  hitherto  unnoticed. 
These  she  compares  by  means  of  the  visual  sense,  since  they  are 
relatively  similar,  and  recognises  them  as  similar  though  such  ob- 
jects are  most  unusual  in  the  bee's  experience. 

5.  Her  poor  olfactory  sense,  which  is  useful  only  at  very  close 
range. 

6.  The  onesidedness  and  narrow  circle  of  her  attention. 

7.  The  rapid  formation  of  habits. 

8.  The  limits  of  imitation  of  bees  by  one  another. 

Of  course,  I  should  not  allow  myself  to  draw  these  conclusions 
from  a  single  experiment,  if  they  had  not  been  confirmed  by  in- 
numerable observations  by  the  ablest  investigators  in  this  field. 
Lubbock  showed  clearly  that  it  is  necessary  to  train  a  bee  for  some 
time  to  go  to  a  particular  color  if  one  wishes  to  compel  her  to  pay 
no  attention  to  other  colors.  This  is  the  only  way  in  which  it  is 
possible  to  demonstrate  her  ability  to  distinguish  colors.  My  bees, 
on  the  contrary,  had  been  trained  on  differently  colored  objects 
(Dahlias  and  artefacts)  and  therefore  paid  no  attention  to  differ- 
ences in  color.  It  would  be  a  fallacy  to  conclude  from  this  that 


28  ANTS  AND  SOME  OTHER  INSECTS. 

they  do  not  distinguish  colors.  On  the  contrary,  by  means  of  other 
experiments  I  have  fully  confirmed  Lubbock's  results. 

By  2.20  P.  M.  all  of  my  bees,  even  the  painted  ones,  had  re- 
turned to  the  Dahlias. 

On  September  27,  a  week  later,  I  wished  to  perform  a  fresh 
experiment  with  the  same  bees.  I  intended  to  make  them  distin- 
guish between  differently  colored  discs,  placed  at  different  points  on 
a  long  scale,  representing  on  a  great  sheet  of  paper,  varying  intensi- 
ties of  light  from  white  through  gray  to  black.  First,  I  wished  to 
train  a  bee  to  a  single  color.  But  I  had  calculated  without  the 
bee's  memory,  which  rendered  the  whole  experiment  impracticable. 
Scarcely  had  I  placed  my  paper  with  the  discs  on  the  lawn  near 
the  Dahlia  bed,  and  placed  one  or  two  bees  on  the  blue  discs  and 
marked  them  with  colors,  when  they  began  to  investigate  all  the 
red,  blue,  white,  black  and  other  discs  with  or  without  honey.  After 
a  few  moments  had  elapsed,  other  bees  came  from  the  Dahlia  bed 
and  in  a  short  time  a  whole  swarm  threw  itself  on  the  paper  discs. 
Of  course,  those  that  had  been  provided  with  honey  were  most  vis- 
ited, because  they  detained  the  bees,  but  even  the  discs  without 
honey  were  stormed  and  scrutinised  by  bees  following  one  another 
in  their  flight.  The  bees  besieged  even  the  paint-box.  Among 
these  there  was  one  that  I  had  previously  deprived  of  her  antennae. 
She  had  previously  partaken  of  the  honey  on  the  blue  discs  and 
had  returned  to  the  hive.  This  bee  examined  the  blue  piece  of 
paint  in  the  color-box. 

In  brief,  my  experiment  was  impossible,  because  all  the  bees 
still  remembered  from  a  former  occasion  the  many-colored  artefacts 
provided  with  honey,  and  therefore  examined  all  the  paper  discs 
no  matter  of  what  color.  The  association  between  the  taste  of  the 
honey  and  the  paper  discs  had  been  again  aroused  by  the  sight- 
perception  of  the  latter,  and  had  acquired  both  consistency  and 
rapid  and  powerful  imitation,  because  honey  happened  to  be  actually 
found  on  some  of  the  discs. 

Together  with  the  perceptive  and  associative  powers,  the 
power  of  drawing  simple,  instinctive  inferences  from  analogy  is 
also  apparent.  Without  this,  indeed,  the  operation  of  perception 


ANTS  AND  SOME  OTHER  INSECTS.  2Q 

and  memory  would  be  inconceivable !  We  have  just  given  an  ex- 
ample. I  have  shown  on  a  former  occasion  that  humble-bees, 
whose  nest  I  had  transferred  to  my  window,  when  they  returned 
home  often  confounded  other  windows  of  the  same  fa$ade  and  ex- 
amined them  for  a  long  time  before  they  discovered  the  right  one. 
Lubbock  reports  similar  facts.  Von  Buttel  shows  that  bees  that 
are  accustomed  to  rooms  and  windows,  learn  to  examine  the  rooms 
and  windows  in  other  places,  i.  e.,  other  houses.  When  Pissot 
suspended  wire  netting  with  meshes  twenty-two  mm.  in  diameter 
in  front  of  a  wasp  nest,  the  wasps  hesitated  at  first,  then  went 
around  the  netting  by  crawling  along  the  ground  or  avoided  it  in 
some  other  way.  But  they  soon  learned  to  fly  directly  through  the 
meshes.  The  sense  of  sight,  observed  during  flight,  is  particularly 
well  adapted  to  experiments  of  this  kind,  which  cannot  therefore 
be  performed  with  ants.  But  the  latter  undoubtedly  draw  similar 
inferences  from  the  data  derived  from  their  topochemical  antennal 
sense.  The  discovery  of  prey  or  other  food  on  a  plant  or  an  ob- 
ject induces  these  insects  to  examine  similar  plants  or  objects  and 
to  perform  other  actions  of  a  like  nature. 

There  are,  on  the  other  hand,  certain  very  stupid  insects,  like 
the  males  of  ants,  the  Diptera  and  may-flies  (Ephemerids)  with 
rudimental  brains,  incapable  of  learning  anything  or  of  combining 
sense-impressions  to  any  higher  degree  than  as  simple  automatisms, 
and  without  any  demonstrable  retention  of  memory-images.  Such 
insects  lead  a  life  almost  exclusively  dominated  by  sensory  stimuli ; 
but  their  lives  are  adapted  to  extremely  simple  conditions.  In 
these  very  instances  the  difference  is  most  striking,  and  they  dem- 
onstrate most  clearly  through  comparison  and  contrast  the  plus 
possessed  by  more  intelligent  insects. 

THE  REALM  OF  WILL. 

The  notion  of  volition,  in  contradistinction  to  the  notion  of 
reflex  action,  presupposes  the  expiration  of  a  certain  time  interval 
and  the  operation  of  mediating  and  complex  brain-activities  be- 
tween the  sense-impression  and  the  movement  which  it  conditions. 
In  the  operation  of  the  purposeful  automatisms  of  instinct  which 


30  ANTS  AND  SOME  OTHER   INSECTS. 

arouse  one  another  into  activity  in  certain  sequences,  there  is  also 
a  time  interval,  filled  out  by  internal,  dynamic  brain-processes  as 
in  the  case  of  the  will.  Hence  these  are  not  pure  reflexes.  They 
may  for  a  time  suffer  interruption  and  then  be  again  continued. 
But  their  operation  is  brought  about  in  great  measure  by  a  con- 
catenation of  complicated  reflexes  which  follow  one  another  in  a 
compulsory  order.  On  this  account  the  term  automatism  or  in- 
stinct is  justifiable. 

If  we  are  to  speak  of  will  in  the  narrower  sense,  we  must  be 
able  to  establish  the  existence  of  individual  decisions,  which  can  be 
directed  according  to  circumstances,  i.  e.,  are  modifiable,  and  may, 
for  a  certain  period,  remain  dormant  in  the  brain  to  be  still  per- 
formed notwithstanding.  Such  volition  may  be  very  different  from 
the  complex  volition  of  man,  which  consists  of  the  resultants  of 
prodigiously  manifold  components  that  have  been  long  preparing 
and  combining.  The  ants  exhibit  positive  and  negative  volitional 
phenomena,  which  cannot  be  mistaken.  The  ants  of  the  genus 
Formica  Linn6  are  particularly  brilliant  in  this  respect,  and  they 
also  illustrate  the  individual  psychical  activities  most  clearly.  The 
above-mentioned  migrations  from  nest  to  nest  show  very  beauti- 
fully the  individual  plans  of  single  workers  carried  out  with  great 
tenacity.  For  hours  at  a  time  an  ant  may  try  to  overcome  a  multi- 
tude of  difficulties  for  the  purpose  of  attaining  an  aim  which  she 
has  set  herself.  This  aim  is  not  accurately  prescribed  by  instinct, 
as  the  insect  may  be  confronted  with  several  possibilities,  so  that 
it  often  happens  that  two  ants  may  be  working  in  opposition  to 
each  other.  This  looks  like  stupidity  to  the  superficial  observer. 
But  it  is  just  here  that  the  ant's  plasticity  reveals  itself.  For  a 
time  the  two  little  animals  interfere  with  each  other,  but  finally 
they  notice  the  fact,  and  one  of  them  gives  in,  goes  away,  or  assists 
the  other. 

These  conditions  are  best  observed  during  the  building  of  nests 
or  roads,  e.  g. ,  in  the  horse-ant  {Formica  rufa)  and  still  better  in 
F.  pratensis.  It  is  necessary,  however,  to  follow  the  behavior  of  a 
few  ants  for  hours,  if  one  would  have  a  clear  conception  of  this 
matter,  and  for  this  much  patience  and  much  time  are  necessary. 


ANTS  AND  SOME  OTHER  INSECTS.  JI 

The  combats  between  ants,  too,  show  certain  very  consistent  aims 
of  behavior,  especially  the  struggles  which  I  have  called  chronic 
combats  {combats  afroid~).  After  two  parties  (two  colonies  brought 
together)  have  made  peace  with  each  other,  one  often  sees  a  few 
individuals  persecuting  and  maltreating  certain  individuals  of  the 
opposite  party.  They  often  carry  their  victims  a  long  distance  off, 
for  the  purpose  of  excluding  them  from  the  nest.  If  the  ant  that 
has  been  borne  away  returns  to  the  nest  and  is  found  by  her  perse- 
cutrix,  she  is  again  seized  and  carried  away  to  a  still  greater  dis- 
tance. In  one  such  case  in  an  artificial  nest  of  a  small  species  of 
Leptothorax,  the  persecuting  ant  succeeded  in  dragging  her  victim 
to  the  edge  of  my  table.  She  then  stretched  out  her  head  and 
allowed  her  burden  to  fall  on  the  floor.  This  was  not  chance,  for 
she  repeated  the  performance  twice  in  succession  after  I  had  again 
placed  the  victim  on  the  table.  Among  the  different  individuals  of 
the  previously  hostile,  but  now  pacified  opposition,  she  had  con- 
centrated her  antipathy  on  this  particular  ant  and  had  tried  to  make 
her  return  to  the  nest  impossible.  One  must  have  very  strong  pre- 
conceived opinions  if  in  such  and  many  similar  cases  one  would 
maintain  that  ants  are  lacking  in  individual  decision  and  execution. 
Of  course,  all  these  things  happen  within  the  confines  of  the  in- 
stinct-precincts of  the  species,  and  the  different  stages  in  the  exe- 
tion  of  a  project  are  instinctive.  Moreover,  I  expressly  defend  my- 
self against  the  imputation  that  I  am  importing  human  reflection 
and  abstract  concepts  into  this  volition  of  the  ant,  though  we  must 
honestly  admit,  nevertheless,  that  in  the  accomplishment  of  our 
human  decisions  both  hereditary  and  secondary  automatisms  are 
permitted  to  pass  unnoticed.  While  I  am  writing  these  words,  my 
eyes  operate  with  partially  hereditary,  and  my  hand  with  secondary 
automatisms.  But  it  goes  without  saying  that  only  a  human  brain 
is  capable  of  carrying  out  my  complex  innervations  and  my  con- 
comitant abstract  reflections.  But  the  ant  must,  nevertheless,  as- 
sociate and  consider  somewhat  in  a  concrete  way  after  the  manner 
of  an  ant,  when  it  pursues  one  of  the  above-mentioned  aims  and 
combines  its  instincts  with  this  special  object  in  view.  While, 
however,  the  instinct  of  the  ant  can  be  combined  for  only  a  few 


32  ANTS  AND  SOME  OTHER  INSECTS. 

slightly  different  purposes,  by  means  of  a  small  number  of  plastic 
adaptations  or  associations,  individually  interrupted  in  their  con- 
catenation or  vice  versa,  in  the  thinking  human  being  both  inherited 
and  secondary  automatisms  are  only  fragments  or  instruments  in 
the  service  of  an  overwhelming,  all-controlling,  plastic  brain-activ- 
ity. It  may  be  said  incidentally  that  the  relative  independence  of 
the  spinal  chord  and  of  subordinate  brain-centers  in  the  lower  ani- 
mals (and  even  in  the  lower  mammals)  as  compared  with  the  cere- 
brum, may  be  explained  in  a  similar  manner  if  they  are  compared 
with  the  profound  dependence  of  these  organs  and  their  functions 
on  the  massive  cerebrum  in  man  and  even  to  some  extent  in  the 
apes.  The  cerebrum  splits  up  and  controls  its  automatisms  (divide 
et  imp  era). 

While  success  visibly  heightens  both  the  audacity  and  tenacity 
of  the  ant-will,  it  is  possible  to  observe  after  repeated  failure  or  in 
consequence  of  the  sudden  and  unexpected  attacks  of  powerful  en- 
emies a  form  of  abulic  dejection,  which  may  lead  to  a  neglect  of 
the  most  important  instincts,  to  cowardly  flight,  to  the  devouring 
or  casting  away  of  offspring,  to  neglect  of  work,  and  similar  condi- 
tions. There  is  a  chronically  cumulative  discouragement  in  degen- 
erate ant-colonies  and  an  acute  discouragement  when  a  combat  is 
lost.  In  the  latter  case  one  may  see  troops  of  large  powerful  ants 
fleeing  before  a  single  enemy,  without  even  attempting  to  defend 
themselves,  whereas  the  latter  a  few  moments  previously  would 
have  been  killed  by  a  few  bites  from  the  fleeing  individuals.  It  is 
remarkable  how  soon  the  victor  notices  and  utilises  this  abulic  dis- 
couragement. The  dejected  ants  usually  rally  after  the  flight  and 
soon  take  heart  and  initiative  again.  But  they  offer  but  feeble  re- 
sistance, e.  g.,  to  a  renewed  attack  from  the  same  enemy  on  the 
following  day.  Even  an  ant's  brain  does  not  so  soon  forget  the 
defeats  which  it  has  suffered. 

In  bitter  conflicts  between  two  colonies  of  nearly  equal  strength 
the  tenacity  of  the  struggle  and  with  it  the  will  to  conquer  increases 
till  one  of  the  parties  is  definitively  overpowered.  In  the  realm  of 
will  imitation  plays  a  great  role.  Even  among  ants  protervity  and 
dejection  are  singularly  contagious. 


ANTS  AND  SOME  OTHER  INSECTS.  33 


THE  REALM  OF  FEELING. 

It  may  perhaps  sound  ludicrous  to  speak  of  feelings  in  insects. 
But  when  we  stop  to  consider  how  profoundly  instinctive  and 
fixed  is  our  human  life  of  feeling,  how  pronounced  are  the  emotions 
in  our  domestic  animals,  and  how  closely  interwoven  with  the  im- 
pulses, we  should  expect  to  encounter  emotions  and  feelings  in 
animal  psychology.  And  these  may  indeed  be  recognised  so  clearly 
that  even  Uexkuell  would  have  to  capitulate  if  he  should  come  to 
know  them  more  accurately.  We  find  them  already  interwoven 
with  the  will  as  we  have  described  it.  Most  of  the  emotions  of  in- 
sects are  profoundly  united  to  the  instincts.  Of  such  a  nature  is 
the  jealousy  of  the  queen  bee  when  she  kills  the  rival  princesses, 
and  the  terror  of  the  latter  while  they  are  still  within  their  cells ; 
such  is  the  rage  of  fighting  ants,  wasps,  and  bees,  the  above-men- 
tioned discouragement,  the  love  of  the  brood,  the  self-devotion  of 
the  worker  honey-bees,  when  they  die  of  hunger  while  feeding  their 
queen,  and  many  other  cases  of  a  similar  description.  But  there 
are  also  individual  emotions  that  are  not  compelled  altogether  by 
instinct,  e.  g.,  the  above-mentioned  mania  of  certain  ants  for  mal- 
treating some  of  their  antagonists.  On  the  other  hand,  as  I  have 
shown,  friendly  services  (feeding),  under  exceptional  circum- 
stances, may  call  forth  feelings  of  sympathy  and  finally  of  partner- 
ship, even  between  ants  of  differents  species.  Further  than  this, 
feelings  of  sympathy,  antipathy,  and  anger  among  ants  may  be  in- 
tensified by  repetition  and  by  the  corresponding  activities,  just  as 
in  other  animals  and  man. 

The  social  sense  of  duty  is  instinctive  in  ants,  though  they  ex- 
hibit great  individual,  temporary,  and  occasional  deviations,  which 
betray  a  certain  amount  of  plasticity. 

PSYCHIC  CORRELATIONS. 

I  have  rapidly  reviewed  the  three  main  realms  of  ant-psychol- 
ogy. It  is  self-evident  that  in  this  matter  they  no  more  admit  of 


34  ANTS  AND  SOME  OTHER  INSECTS. 

sharp  demarcation  from  one  another  than  elsewhere.  The  will 
consists  of  centrifugal  resultants  of  sense-impressions  and  feelings 
and  in  turn  reacts  powerfully  on  both  of  these. 

It  is  of  considerable  interest  to  observe  the  antagonism  be- 
tween different  perceptions,  feelings,  and  volitions  in  ants  and 
bees,  and  the  manner  in  which  in  these  animals  the  intensely  fixed 
(obsessional)  attention  may  be  finally  diverted  from  one  thing  to 
another.  Here  experiment  is  able  to  teach  us  much.  While  bees 
are  busy  foraging  on  only  one  species  of  flower,  they  overlook 
everything  else,  even  other  flowers.  If  their  attention  is  diverted 
by  honey  offered  them  directly,  although  previously  overlooked, 
they  have  eyes  only  for  the  honey.  An  intense  emotion,  like  the 
swarming  of  honey-bees  (von  Buttel)  compells  these  insects  to 
forget  all  animosities  and  even  the  old  maternal  hive  to  which  they 
no  longer  return.  But  if  the  latter  happens  to  be  painted  blue, 
and  if  the  swarming  is  interrupted  by  taking  away  the  queen,  the 
bees  recollect  the  blue  color  of  their  old  hive  and  fly  to  hives  that 
are  painted  blue.  Two  feelings  often  struggle  with  each  other  in 
bees  that  are  "crying"  and  without  a  queen:  that  of  animosity 
towards  strange  bees  and  the  desire  for  a  queen.  Now  if  they  be 
given  a  strange  queen  by  artificial  means,  they  kill  or  maltreat  her, 
because  the  former  feeling  at  first  predominates.  For  this  reason 
the  apiarist  encloses  the  strange  queen  in  a  wire  cage.  Then  the 
foreign  odor  annoys  the  bees  less  because  it  is  further  away  and 
they  are  unable  to  persecute  the  queen.  Still  they  recognise  the 
specific  queen-odor  and  are  able  to  feed  her  through  the  bars  of  the 
cage.  This  suffices  to  pacify  the  hive.  Then  the  second  feeling 
quickly  comes  to  the  front ;  the  workers  become  rapidly  inured  to 
the  new  odor  and  after  three  or  four  days  have  elapsed,  the  queen 
may  be  liberated  without  peril. 

It  is  possible  in  ants  to  make  the  love  of  sweets  struggle  with 
the  sense  of  duty,  when  enemies  are  made  to  attack  a  colony  and 
honey  is  placed  before  the  ants  streaming  forth  to  defend  their 
nest.  I  have  done  this  with  Formica  pratensis.  At  first  the  ants 
partook  of  the  honey,  but  only  for  an  instant.  The  sense  of  duty 
conquered  and  all  of  them  without  exception,  hurried  forth  to  battle 


ANTS  AND  SOME  OTHER  INSECTS.  35 

and  most  of  them  to  death.     In  this  case  a  higher  decision  of  in- 
stinct was  victorious  over  the  lower  impulse. 

In  r/sumJ  I  would  lay  stress  on  the  following  general  conclu- 
sions : 

1.  From  the  standpoint  of  natural  science  we  are  bound  to 
hold  fast  to  the  psychophysiological  theory  of  identity  (Monism)  in 
contradistinction  to  dualism,  because  it  alone  is  in  harmony  with 
the  facts  and  with  the  law  of  the  conservation  of  energy. 

Our  mind  must  be  studied  simultaneously  both  directly  from 
within  and  indirectly  from  without,  through  biology  and  the  condi- 
tions of  its  origin.  Hence  there  is  such  a  thing  as  comparative 
psychology  of  other  individuals  in  addition  to  that  of  self,  and  in 
like  manner  we  are  led  to  a  psychology  of  animals.  Inference  from 
analogy,  applied  with  caution,  is  not  only  permissible  in  this  sci- 
ence, but  obligatory. 

2.  The  senses  of  insects  are  our  own.    Only  the  auditory  sense 
still  remains  doubtful,  so  far  as  its  location  and  interpretation  are 
concerned.     A  sixth  sense  has  not  yet  been  shown  to  exist,  and  a 
special  sense  of  direction  and  orientation  is  certainly  lacking.    The 
vestibular  apparatus  of  vertebrates  is  merely  an  organ  of  equilibra- 
tion and  mediates  internal  sensations  of  acceleration,  but  gives  no 
orientation  in  space  outside  of  the  body.     On  the  other  hand  the 
visual  and  olfactory  senses  of  insects  present  varieties  in  the  range 
of  their  competency  and  in  their  specific  energies  (vision  of  ultra- 
violet, functional  peculiarities  of  the  facetted  eye,  topochemical 
antennal  sense  and  contact-odor). 

3.  Reflexes,  instincts,  and  plastic,  individually  adaptive,  cen- 
tral nervous  activities  pass  over  into  one  another  by  gradations. 
Higher  complications  of  these  central  or  psychic  functions  corre- 
spond to  a  more  complicated  apparatus  of  superordinated  neuron- 
complexes  (cerebrum). 

4.  Without  becoming   antagonistic,  the  central  nervous  activ- 
ity in  the  different  groups  and  species  of  animals  complicates  itself 
in  two  directions:   (0)  through  inheritance  (natural  selection,  etc.) 
of  the  complex,  purposeful  automatisms,  or  instincts  ;  (l>)  through 
the  increasingly  manifold  possibilities  of  plastic,  individually  adap- 


36  ANTS  AND  SOME  OTHER  INSECTS. 

tive  activities,  in  combination  with  the  faculty  of  gradually  devel- 
oping secondary  individual  automatisms  (habits). 

The  latter  mode  requires  many  more  nerve-elements.  Through 
hereditary  predispositions  (imperfect  instincts)  of  greater  or  less 
stability,  it  presents  transitions  to  the  former  mode. 

5.  In  social  insects  the  correlation  of  more  developed  psychic 
powers  with  the  volume  of  the  brain  may  be  directly  observed. 

6.  In  these  animals  it  is  possible  to  demonstrate  the  existence 
of  memory,  associations  of  sensory  images,  perceptions,  attention, 
habits,  simple  powers  of  inference  from  analogy,  the  utilisation  of 
individual  experiences  and  hence  distinct,  though  feeble,  plastic, 
individual  deliberations  or  adaptations. 

7.  It  is  also  possible  to   detect  a  corresponding,  simpler  form 
of  volition,  i.  e.,  the  carrying  out  of  individual  decisions  in  a  more 
or  less  protracted  time-sequence,  through  different  concatenations 
of  instincts ;  furthermore  different  kinds  of  discomfort  and  pleasure 
emotions,  as  well  as  interactions  and  antagonisms  between  these  di- 
verse psychic  powers. 

8.  In  insect  behavior  the  activity  of  the  attention  is  one-sided 
and  occupies  a  prominent  place.     It  narrows  the  scope  of  behavior 
and  renders  the  animal  temporarily  blind  (inattentive)  to  other 
sense-impressions. 

Thus,  however  different  may  be  the  development  of  the  auto- 
matic and  plastic,  central  neurocyme  activities  in  the  brains  of  dif- 
ferent animals,  it  is  surely  possible,  nevertheless,  to  recognise  cer- 
tain generally  valid  series  of  phenomena  and  their  fundamental 
laws. 

Even  to-day  I  am  compelled  to  uphold  the  seventh  thesis 
which  I  established  in  1877  in  my  habilitation  as  privat-docent  in 
the  University  of  Munich  : 

"All  the  properties  of  the  human  mind  may  be  derived  from 
the  properties  of  the  animal  mind." 

I  would  merely  add  to  this  : 

"And  all  the  mental  attributes  of  higher  animals  may  be  de- 
rived from  those  of  lower  animals."  In  other  words :  The  doctrine 
of  evolution  is  quite  as  valid  in  the  province  of  psychology  as  it  is 


ANTS  AND  SOME  OTHER  INSECTS.  37 

in  all  the  other  provinces  of  organic  life.  Notwithstanding  all  the 
differences  presented  by  animal  organisms  and  the  conditions  of 
their  existence,  the  psychic  functions  of  the  nerve-elements  seem 
nevertheless,  everywhere  to  be  in  accord  with  certain  fundamental 
laws,  even  in  the  cases  where  this  would  be  least  expected  on  ac- 
count of  the  magnitude  of  the  differences. 


APPENDIX. 
THE  PECULIARITIES  OF  THE  OLFACTORY  SENSE  IN  INSECTS. 

Our  sense  of  smell,  like  our  sense  of  taste,  is  a  chemical  sense. 
But  while  the  latter  reacts  only  to  substances  dissolved  in  liquids 
and  with  but  few  (about  five)  different  principal  qualities,  the 
olfactory  sense  reacts  with  innumerable  qualities  to  particles  of  the 
most  diverse  substances  dissolved  in  the  atmosphere.  Kven  to  our 
relatively  degenerate  human  olfactories,  the  number  of  these  odor- 
qualities  seems  to  be  almost  infinite. 

In  insects  that  live  in  the  air  and  on  the  earth  the  sense  of 
taste  seems  to  be  located,  not  only  like  our  own,  in  the  mouth- 
parts,  but  also  to  exhibit  the  same  qualities  and  the  corresponding 
reactions.  At  any  rate  it  is  easy  to  show  that  these  animals  are 
usually  very  fond  of  sweet,  and  dislike  bitter  things,  and  that  they 
perceive  these  two  properties  only  after  having  tasted  of  the  re- 
spective substances.  F.  Will,  in  particular,  has  published  good 
experiments  on  this  subject. 

In  aquatic  insects  the  conditions  are  more  complicated.  Nagel, 
who  studied  them  more  closely,  shows  how  difficult  it  is  in  these 
cases  to  distinguish  smell  from  taste,  since  substances  dissolved  in 
water  are  more  or  less  clearly  perceived  or  discerned  from  a  dis- 
tance by  both  senses  and  sought  or  avoided  in  consequence.  Nagel, 
at  any  rate,  succeeded  in  showing  that  the  palpi,  which  are  of  less 
importance  in  terrestrial  insects,  have  an  important  function  in 
aquatic  forms. 

In  this  place  we  are  concerned  with  an  investigation  of  the 
sense  of  smell  in  terrestrial  insects.  Its  seat  has  been  proved  to  be 


38  ANTS  AND  SOME  OTHER  INSECTS. 

in  the  antennae.  A  less  important  adjunct  to  these  organs  is  located, 
as  Nagel  and  Wasmann  have  shown,  in  the  palpi.  In  the  antennae 
it  is  usually  the  club  or  foliaceous  or  otherwise  formed  dilatations 
which  accommodate  the  cellular  ganglion  of  the  antennary  nerve. 
I  shall  not  discuss  the  histological  structure  of  the  nerve-termina- 
tions but  refer  instead  to  Hicks,  Leydig,  Hauser,  my  own  investi- 
gations and  the  other  pertinent  literature,  especially  to  K.  Kraepe- 
lin's  excellent  work.  I  would  merely  emphasise  the  following 
points: 

1.  All  the  olfactory  papillae  of  the  antennae  are  transformed, 
hair-like  pore-canals. 

2.  All  of  these  present  a  cellular  dilatation  just  in  front  of  the 
nerve-termination. 

3.  Tactile  hairs  are  found  on  the  antennae  together  with  the 
olfactory  papillae. 

4.  The  character  and  form  of  the  nerve-terminations  are  highly 
variable,  but  they  may  be  reduced  to  three  principal  types:  pore- 
plates,   olfactory  rods,   and  olfactory  hairs.     The  two  latter  are 
often  nearly  or  quite  indistinguishable  from  each  other.   The  nerve- 
termination  is  always  covered  with  a  cuticula  which  may  be  never 
so  delicate. 

Other  end-organs  of  the  Hymenopteran  antenna  described  by 
Hicks  and  myself,  are  still  entirely  obscure,  so  far  as  their  function 
is  concerned,  but  they  can  have  nothing  to  do  with  the  sense  of 
smell,  since  they  are  absent  in  insects  with  a  delicate  sense  of  smell 
(wasps)  and  accur  in  great  numbers  in  the  honey-bees,  which  have 
obtuse  olfactories. 

That  the  antennae  and  not  the  nerve-terminations  of  the  mouth 
and  palate  function,  as  organs  of  smell,  has  been  demonstrated  by 
my  control  experiments,  which  leave  absolutely  no  grounds  for 
doubt  and  have,  moreover,  been  corroborated  on  all  sides.  Ter- 
restrial insects  can  discern  chemical  substances  at  a  distance  by 
means  of  their  antennae  only.  But  in  touch,  too,  these  organs  are 
most  important  and  the  palpi  only  to  a  subordinate  extent,  namely 
in  mastication.  The  antennae  enable  the  insect  to  perceive  the 
chemical  nature  of  bodies  and  in  particular,  to  recognise  and  dis- 


ANTS  AND  SOME  OTHER  INSECTS.  39 

tinguish  plants,  other  animals  and  food,  except  in  so  far  as  the 
visual  and  gustatory  senses  are  concerned  in  these  activities.  These 
two  senses  may  be  readily  eliminated,  however,  since  the  latter 
functions  only  during  feeding  and  the  former  can  be  removed  by 
varnishing  the  eyes  or  by  other  means.  Many  insects,  too,  are 
blind  and  find  their  way  about  exclusively  by  means  of  their  an- 
tennae. This  is  the  case,  e.  g.,  with  many  predatory  ants  of  the 
genus  Eciton. 

But  I  will  here  assume  these  questions  to  be  known  and  an- 
swered, nor  will  I  indulge  in  polemics  with  Bethe  and  his  asso- 
ciates concerning  the  propriety  of  designating  the  chemical  anten- 
nal  sense  as  "smell."  I  have  discussed  this  matter  elsewhere.1 
What  I  wish  to  investigate  in  this  place  is  the  psychological  quality 
of  the  antennal  olfactory  sense,  how  it  results  in  part  from  observa- 
tion and  in  part  from  the  too  little  heeded  correlative  laws  of  the 
psychological  exploitation  of  each  sense  in  accordance  with  its 
structure.  I  assume  as  known  the  doctrines  of  specific  energies 
and  adequate  stimuli,  together  with  the  more  recent  investigations 
on  the  still  undifferentiated  senses,  like  photodermatism  and  the 
like,  and  would  refer,  moreover,  to  Helmholtz's  Die  Thatsachen  in 
der  Wahrnehmung,  1879.  Hirschwald,  Berlin. 

When  in  our  own  human  subjective  psychology,  which  alone 
is  known  to  us  directly,  we  investigate  the  manner  in  which  we  in- 
terpret our  sensations,  we  happen  upon  a  peculiar  fact  to  which 
especially  Herbert  Spencer  has  called  attention.  We  find  that  so- 
called  perceptions  consist,  as  is  well  known,  of  sensations  which 
are  bound  together  sometimes  firmly,  sometimes  more  loosely.  The 
more  intimately  the  sensations  are  bound  together  to  form  a  whole, 
the  easier  it  is  for  us  to  recall  in  our  memory  the  whole  from  a 
part.  Thus,  e.  g.,  it  is  easy  for  me  to  form  an  idea  from  the  thought 
of  the  head  of  an  acquaintance  as  to  the  remainder  of  his  body.  In 
the  same  manner  the  first  note  of  a  melody  or  the  first  verse  of  a 
poem  brings  back  the  remainder  of  either.  But  the  thought  of  an 

1 "  Sensations  des  Insectes,"  Kivista  di  Biologia  Generale.  Como,  1900-1901. 
For  the  remainder  see  also  A.  Forel,  Mitth.  des  MUnchener  entom.  Vercins,  1878, 
and  Kccueil.  Zool.  Sut'sse,  1886-1887. 


4o 


ANTS  AND  SOME  OTHER  INSECTS. 


odor  of  violets,  a  sensation  of  hunger,  or  a  stomach-ache,  are  in- 
capable of  recalling  in  me  either  simultaneous  or  subsequent  odors 
or  feelings. 

These  latter  conditions  call  up  in  my  consciousness  much 
more  easily  certain  associated  visual,  tactile,  or  auditory  images 
(e.  g.,  the  visual  image  of  a  violet,  a  table  set  for  a  meal).  As 
ideas  they  are  commonly  to  be  represented  in  consciousness  only 
with  considerable  difficulty,  and  sometimes  not  at  all,  and  they  are 
scarcely  capable  of  association  among  themselves.  We  readily  ob- 
serve, moreover,  that  visual  images  furnish  us  mainly  with  space 
recollections,  auditory  images  with  sequences  in  time,  and  tactile 
images  with  both,  but  less  perfectly.  These  are  indubitable  and 
well-known  facts. 

But  when  we  seek  for  the  wherefore  of  these  phenomena,  we 
find  the  answer  in  the  structure  of  the  particular  sense-organ  and 
in  its  manner  of  functioning. 

It  is  well  known  that  the  eye  gives  us  a  very  accurate  image 
of  the  external  world  on  our  retina.  Colors  and  forms  are  there 
depicted  in  the  most  delicate  detail,  and  both  the  convergence  of 
our  two  eyes  and  their  movement  and  accommodation  gives  us  be- 
sides the  dimensions  of  depth  through  stereoscopic  vision.  What- 
ever may  be  still  lacking  or  disturbing  is  supplied  by  instinctive 
inferences  acquired  by  practice,  both  in  memory  and  direct  per- 
ception (like  the  lacunae  of  the  visual  field),  or  ignored  (like  the 
turbidity  of  the  corpus  vitreum).  But  the  basis  of  the  visual  im- 
age is  given  in  the  coordinated  tout  ensemble  of  the  retinal  stimuli, 
namely  the  retinal  image.1  Hence,  since  the  retina  furnishes  us 
with  such  spatial  projections,  and  these  in  sharp  details,  or  rela- 
tions, definitely  coordinated  with  one  another,  the  sense  of  sight 
gives  us  knowledge  of  space.  For  this  reason,  also,  and  solely  on 
this  account,  we  find  it  so  easy  to  supply  through  memory  by  asso- 


1  It  is  well  known  that  in  this  matter  the  movements  of  the  eyes,  the  move- 
ments of  the  body  and  of  external  objects  play  an  essential  part,  so  that  without 
these  the  eye  would  fail  to  give  us  any  knowledge  of  space.  But  I  need  not  discuss 
this  further,  since  the  antennae  of  ants  are  at  least  quite  as  moveable  and  their 
olfactory  sense  is  even  more  easily  educated  in  unison  with  the  tactile  sense. 


ANTS  AND  SOME  OTHER  INSECTS.  4! 

ciation  the  missing  remnant  of  a  visual  spatial  image.  For  this 
reason,  too,  the  visual  sensations  are  preeminently  associative  or 
relational  in  space,  to  use  Spencer's  expression.  For  the  same 
reason  the  insane  person  so  readily  exhibits  halucinations  of  com- 
plicated spatial  images  in  the  visual  sphere.  This  would  be  im- 
possible in  the  case  of  the  olfactory  sense. 

Similarly,  the  organ  of  Corti  in  the  ear  gives  us  tone  or  sound 
scales  in  accurate  time-sequence,  and  hence  also  associations  of 
sequence  much  more  perfectly  than  the  other  senses.  Its  associa- 
tions are  thus  in  the  main  associations  of  sequence,  because  the 
end-apparatus  registers  time-sequences  in  time-intervals  and  not 
as  space  images. 

The  corresponding  cortical  receptive  areas  are  capable,  in  the 
first  instance,  merely  of  registering  what  is  brought  to  them  by  the 
sense-stimuli  and  these  are  mainly  associated  spatial  images  for 
sight  and  tone  or  sound-sequences  for  hearing. 

Let  us  consider  for  a  moment  how  odors  strike  the  mucous 
membranes  of  our  choanas.  They  are  wafted  towards  us  as  wild 
mixtures  in  an  airy  maelstrom,  which  brings  them  to  the  olfactory 
terminations  without  order  in  the  inhaled  air  or  in  the  mucous  of 
the  palate.  They  come  in  such  a  way  that  there  cannot  possibly 
be  any  spatial  association  of  the  different  odors  in  definite  relation- 
ships. In  time  they  succeed  one  another  slowly  and  without  order, 
according  to  the  law  of  the  stronger  element  in  the  mixture,  but 
without  any  definite  combination.  If,  after  one  has  been  inhaling 
the  odor  of  violets,  the  atmosphere  gradually  becomes  charged 
with  more  roast  meat  than  violet  particles,  the  odor  of  roast  suc- 
ceeds that  of  violet.  But  nowhere  can  we  perceive  anything  like  a 
definitely  associated  sequence,  so  that  neither  our  ideas  of  time  nor 
those  of  space  comprise  odors  that  revive  one  another  through  as- 
sociation. By  much  sniffing  of  the  surface  of  objects  we  could  at 
most  finally  succeed  in  forming  a  kind  of  spatial  image,  but  this 
would  be  very  difficult  owing  to  man's  upright  posture.  Neverthe- 
less it  is  probable  that  dogs,  hedge-hogs,  and  similar  animals  ac- 
quire a  certain  olfactory  image  by  means  of  sniffing.  The  same 
conditions  obtain  in  the  sphere  of  taste  and  the  visceral  sensations 


42  ANTS  AND  SOME  OTHER  INSECTS. 

for  the  same  reasons.  None  of  these  senses  furnish  us  with  any 
sharply  defined  qualitative  relations  either  in  space  or  time.  On 
this  account  they  furnish  by  themselves  no  associations,  no  true 
perceptions,  no  memory  images,  but  merely  sensations,  and  these 
often  as  mixed  sensations,  which  are  vague  and  capable  of  being 
associated  only  with  associative  senses.  The  hallucinations  of 
smell,  taste,  and  of  the  splanchnic  sensations,  are  not  deceptive 
perceptions,  since  they  cannot  have  a  deceptive  resemblance  to  ob- 
jects. They  are  simply  paraesthesias  or  hyperaesthesias,  i.  e.,  path- 
ological sensations  of  an  elementary  character  either  without  ade- 
quate stimulus  or  inadequate  to  the  stimulus. 

The  tactile  sense  furnishes  us  with  a  gross  perception  of  space 
and  of  definite  relations,  and  may,  therefore,  give  rise  to  hallucina- 
tions, or  false  perceptions  of  objects.  By  better  training  its  asso- 
ciative powers  in  the  blind  may  be  intensified.  The  visual  sensa- 
tions are  usually  associated  with  tactile  localisations. 

Thus  we  see  that  there  is  a  law  according  to  which  the  psy- 
chology of  a  sense  depends  not  only  on  its  specific  energy  but  also 
on  the  manner  in  which  it  is  able  to  transmit  to  the  brain  the  rela- 
tions of  its  qualities  in  space  and  time.  On  this  depends  the 
knowledge  we  acquire  concerning  time  and  space  relations  through 
a  particular  sense  and  hence  also  its  ability  to  form  perceptions 
and  associations  in  the  brain.  More  or  less  experience  is,  of  course, 
to  be  added  or  subtracted,  but  this  is  merely  capable  of  enriching 
the  knowledge  of  its  possessor  according  to  the  measure  of  the  re- 
lations of  the  particular  sense-stimuli  in  space  and  time. 

I  would  beg  you  to  hold  fast  to  what  I  have  said  and  then  to 
picture  to  yourselves  an  olfactory  sense,  i.  e.,  a  chemical  sense 
effective  at  a  distance  and  like  our  sense  of  smell,  capable  of  re- 
ceiving impressions  from  particles  of  the  most  diverse  substances 
diffused  through  the  atmosphere,  located  not  in  your  nostrils,  but 
on  your  hands.  For  of  such  a  nature  is  the  position  of  the  olfac- 
tory sense  on  the  antennal  club  of  the  ant. 

Now  imagine  your  olfactory  hands  in  continual  vibration,  touch- 
ing all  objects  to  the  right  and  to  the  left  as  you  walk  along,  thereby 
rapidly  locating  the  position  of  all  odoriferous  objects  as  you  ap- 


ANTS  AND  SOME  OTHER  INSECTS.  43 

proach  or  recede  from  them,  and  perceiving  the  surfaces  both  simul- 
taneously and  successively  as  parts  of  objects  differing  in  odor  and 
position.  It  is  clear  from  the  very  outset  that  such  sense-organs 
would  enable  you  to  construct  a  veritable  odor-chart  of  the  path 
you  had  traversed  and  one  of  double  significance : 

1.  A  clear  contact-odor  chart,  restricted,   to  be  sure,  to  the 
immediate  environment  and  giving  the  accurate  odor-form  of  the 
objects  touched  (round  odors,  rectangular  odors,  elongate  odors, 
etc.)  and  further  hard  and  soft  odors  in  combination  with  the  tac- 
tile sensations. 

2.  A  less  definite  chart  which,  however,  has  orienting  value 
for  a  certain  distance,  and  produces  emanations  which  we  may  pic- 
ture to  ourselves  like  the  red  gas  of  bromine  which  we  can  actually 
see. 

If  we  have  demonstrated  that  ants  perceive  chemical  qualities 
through  their  antennae  both  from  contact  and  from  a  distance,  then 
the  antennae  must  give  them  knowledge  of  space,  if  the  above  for- 
mulated law  is  true,  and  concerning  this  there  can  be  little  doubt. 
This  must  be  true  even  from  the  fact  that  the  two  antennae  simul- 
taneously perceive  different  and  differently  odoriferous  portions  of 
space.1 

They  must  therefore  also  transmit  perceptions  and  topograph- 
ically associated  memories  concerning  a  path  thus  touched  and 
smelled.  Both  the  trail  of  the  ants  themselves  and  the  surround- 
ing objects  must  leave  in  their  brains  a  chemical  (odor-)  space- 
form  with  different,  more  or  less  definitely  circumscribed  qualities, 
i.  e.,  an  odor-image  of  immediate  space,  and  this  must  render  as- 
sociated memories  possible.  Thus  an  ant  must  perceive  the  forms 
of  its  trail  by  means  of  smell.  This  is  impossible,  at  least  for  the 
majority  of  the  species,  by  means  of  the  eyes.  If  this  is  true,  an 
ant  will  always  be  able,  no  matter  where  she  may  be  placed  on  her 

1  It  is  not  without  interest  to  compare  these  facts  with  Condillac's  discussion 
( Treatise  on  the  Sensations)  concerning  his  hypothetical  statue.  Condillac  shows 
that  our  sense  of  smell  is  of  itself  incapable  of  giving  us  space  knowledge.  But  it 
is  different  in  the  case  of  the  topochemical  sense  of  smell  in  combination  with  the 
antennary  movements.  Here  Condillac's  conditions  of  the  gustatory  sense  are  ful- 
filled. 


44  ANTS  AND  SOME  OTHER  INSECTS. 

trail,  to  perceive  what  is  to  the  right,  left,  behind  or  before  her, 
and  consequently  what  direction  she  is  to  take,  according  to  whether 
she  is  bound  for  home,  or  in  the  opposite  direction  to  a  tree  in- 
fested with  Aphides,  or  the  like. 

Singularly  enough,  I  had  established  this  latter  fact  in  my 
"Etudes  Myrme"cologiques  en  1886"  (Annales  de  la  Societt  Ento- 
mologique  de  Belgique}  before  I  had  arrived  at  its  theoretical  inter- 
pretation. But  I  was  at  once  led  by  this  discovery  in  the  same 
work  to  the  interpretation  just  given.  Without  knowing  of  my 
work  in  this  connection,  A.  Bethe  has  recently  established  (dis- 
covered, as  he  supposes)  this  same  fact,  and  has  designated  it  as 
"polarisation  of  the  ant-trail."  He  regards  this  as  the  expression 
of  a  mysterious,  inexplicable  force,  or  polarisation.  As  we  have 
seen,  the  matter  is  not  only  no  enigma,  but  on  the  contrary,  a  nec- 
essary psychological  postulate.  We  should  rather  find  the  absence 
of  this  faculty  incomprehensible. 

But  everything  I  have  just  said  presupposes  a  receptive  brain. 
The  formation  of  lasting  perceptions  and  associations  cannot  take 
place  without  an  organ  capable  of  fixing  the  sense-impressions  and 
of  combining  them  among  themselves.  Experience  shows  that  the 
immediate  sensory  centers  are  inadequate  to  the  performance  of 
this  task.  Though  undoubtedly  receptive,  they  are,  nevertheless, 
incapable  of  utilising  what  has  been  received  in  the  development 
of  more  complex  instincts  and  can  turn  it  to  account  only  in  the 
grosser,  simpler  reflexes  and  automatisms.  To  be  sure,  a  male 
ant  has  better  eyes  than  a  worker  ant,  and  probably  quite  as  good 
antennae,  but  he  is  unable  to  remember  what  he  has  seen  and  is 
especially  incapable  of  associating  it  in  the  form  of  a  trail-image, 
because  he  is  almost  devoid  of  a  brain.  For  this  reason  he  is  un- 
able to  find  his  way  back  to  the  nest.  On  the  other  hand,  it  is  well 
known  that  the  brain  of  a  man  who  has  lost  a  limb  or  whose  hear- 
ing is  defective,  will  enable  him  to  paint  pictures  with  his  foot, 
write  with  the  stump  of  an  arm  or  construct  grand  combinations 
from  the  images  of  defective  senses. 

I  venture,  therefore,  to  designate  as  topochemical  the  olfactory 
antennal  sense  of  honey-bees,  humble-bees,  wasps,  etc. 


ANTS  AND  SOME  OTHER  INSECTS.  45 

Can  we  generalise  to  such  an  extent  as  to  apply  this  term  with- 
out further  investigation  to  all  arthropods?  To  a  considerable  ex- 
tent this  must  be  denied. 

In  fact,  the  multiformity  in  the  structure  and  development  of 
the  arthropod  sense-organs  is  enormous,  and  we  must  exercise  cau- 
tion in  making  premature  generalisations. 

It  is  certain  that  in  some  aerial  insects  the  olfactory  sense  has 
dwindled  to  a  minimum,  e.  g.,  in  those  species  in  which  the  male 
recognises  and  follows  the  female  exclusively  by  means  of  the  eyes, 
as  in  the  Odonata  (dragon-flies).  To  insects  with  such  habits  an 
olfactory  sense  would  be  almost  superfluous.  Here,  too,  the  an- 
tennae have  dwindled  to  diminutive  dimensions. 

But  there  are  insects  whose  antennas  are  immovable  and  quite 
unable  to  touch  objects.  This  is  the  case  in  most  Diptera  (flies). 
Still  these  antennas  are  often  highly  developed  and  present  striking 
dilatations  densely  beset  with  olfactory  papillae.  By  experiment  I 
have  demonstrated  the  existence  of  an  olfactory  sense  in  such 
Dipteran  antennae,  and  I  have  been  able  to  show  that,  e.  g.,  in 
Sarcophaga  vivipara  and  other  carrion  flies,  the  egg-laying  instinct 
is  absolutely  dependent  on  the  sensation  of  the  odor  of  carrion  and 
the  presence  of  the  antennae.  In  these  cases  the  contact-odor  sense 
is  undoubtedly  absent.  More  or  less  of  a  topochemical  odor-sense 
at  long  range  must,  of  course,  be  present,  since  the  antennae  are 
external,  but  the  precision  of  the  spatial  image  must  be  very  im- 
perfect, owing  to  the  immobility  of  the  antennas.  Nevertheless, 
flies  move  about  so  rapidly  in  the  air  that  they  must  be  able  by 
means  of  their  antennae  to  distinguish  very  quickly  the  direction 
from  which  odors  are  being  wafted.  These  insects  do,  in  fact,  find 
the  concealed  source  of  odors  with  great  assurance.  But  this  is  no 
great  art,  for  even  we  ourselves  are  able  to  do  the  same  by  sniffing 
or  going  to  and  fro.  But  the  flies  find  their  way  through  the  air 
with  their  eyes  and  not  at  all  by  means  of  their  sense  of  smell. 
Hence  their  olfactory  powers  probably  constitute  a  closer  psycho- 
logical approximation  to  those  of  mammals  than  to  the  topochemi- 
cal odor-sense  of  ants,  for  they  can  hardly  furnish  any  constant  and 
definite  space-relations. 


46  ANTS  AND  SOME  OTHER  INSECTS. 

Even  in  many  insects  with  movable  antennae  and  of  less  aerial 
habits,  e.  g.,  the  chafers  and  bombycid  moths,  the  antennal  olfac- 
tory sense  is  evidently  much  better  adapted  to  function  at  a  dis- 
tance, i.  e.,  to  the  perception  of  odors  from  distant  objects,  than 
to  the  perception  of  space  and  trails.  Such  insects  find  their  way 
by  means  of  their  eyes,  but  fly  in  the  direction  whence  their  an- 
tennae perceive  an  odor  that  is  being  sought. 

A  genuine  topochemical  antennal  sense  is,  therefore,  probably 
best  developed  in  all  arthropods,  whose  antennae  are  not  only  mov- 
able in  the  atmosphere,  but  adapted  to  feeling  of  objects.  In  these 
cases  the  still  imperfect  topochemical  oder-sense  for  distances  can 
be  momentarily  controlled  by  the  contact-odor-sense  and  defini- 
tively fixed  topographically,  i.  e.,  topochemically,  as  we  see  so  ex- 
tensively practised  in  the  ants. 

It  would  be  possible  to  meet  this  view  with  the  objection  that 
a  contact-odor  sense  could  not  accomplish  much  more  than  the 
tactile  sense.  I  have  made  this  objection  to  myself.  But  in  the 
first  place  it  is  necessary  to  reckon  with  the  facts.  Now  it  is  a  fact 
that  insects  in  touching  objects  with  their  antennae  mainly  perceive 
and  distinguish  the  chemical  constitution  of  the  objects  touched 
and  heed  these  very  much  more  than  they  do  the  mechanical  im- 
pacts also  perceived  at  the  same  time.  Secondly,  the  tactile  sense 
gives  only  resistance  and  through  this,  form.  On  the  other  hand, 
the  multiplicity  of  odors  is  enormous,  and  it  is  possible  to  demon- 
strate, as  I  have  done  for  the  ants,  and  Von  Buttel-Reepen  for  the 
bees,  that  these  animals  in  distinguishing  their  different  nest-mates 
and  their  enemies,  betray  nothing  beyond  the  perception  of  ex- 
tremely delicate  and  numerous  gradations  in  the  qualities  of  odors. 

In  combination  with  topochemical  space-perception,  these 
numerous  odor-qualities  must  constitute  a  spatial  sense  which  is 
vastly  superior  to  the  tactile  sense.  The  whole  biology  of  the  so- 
cial Hymenoptera  furnishes  the  objective  proof  of  this  assertion. 

It  would  certainly  be  well  worth  while  to  investigate  this  mat- 
ter in  other  groups  of  arthropods  which  possess  complex  instincts. 

In  conclusion  I  will  cite  an  example,  which  I  have  myself  ob- 


ANTS  AND  SOME  OTHER  INSECTS.  47 

served,  for  the  purpose  of  illustrating  the  capacity  of  the  topo- 
chemical  olfactory  sense. 

The  American  genus  Eciton  comprises  predatory  ants  that 
build  temporary  nests  from  which  they  undertake  expeditions  for 
the  purpose  of  preying  on  all  kinds  of  insects.  The  Ecitons  follow 
one  another  in  files,  like  geese,  and  are  very  quick  to  detect  new 
hunting  grounds.  As  "ants  of  visitation,"  like  the  Africo-Indian 
species  of  Dorylus,  they  often  take  possession  of  human  dwellings, 
ferret  about  in  all  the  crevices  of  the  walls  and  rooms  for  spiders, 
roaches,  mice,  and  even  rats,  attack  and  tear  to  pieces  all  such 
vermin  in  the  course  of  a  few  hours  and  then  carry  the  booty  home. 
They  can  convert  a  mouse  into  a  clean  skeleton.  They  also  attack 
other  ants  and  plunder  their  nests. 

Now  all  the  workers  of  the  African  species  of  Dorylus  and  of 
many  of  the  species  of  Eciton  are  totally  blind,  so  that  they  must 
orient  themselves  exclusively  by  means  of  their  antennal  sense. 

In  1899  at  Faisons,  North  Carolina,  I  was  fortunate  enough  to 
find  a  temporary  nest  of  the  totally  blind  little  Eciton  carolinense  in 
a  rotten  log.  I  placed  the  ants  in  a  bag  and  made  them  the  sub- 
ject of  some  observations.  The  Eciton  workers  carry  their  elon- 
gate larvae  in  their  jaws  and  extending  back  between  their  legs  in 
such  a  position  that  the  antenna?  have  full  play  in  front. 

Their  ability  to  follow  one  another  and  to  find  their  way  about 
rapidly  and  unanimously  in  new  territory  without  a  single  ant  go- 
ing astray,  is  incredible.  I  threw  a  handful  of  Ecitons  with  their 
young  into  a  strange  garden  in  Washington,  i.  e.,  after  a  long  rail- 
way journey  and  far  away  from  their  nest.  Without  losing  a  mo- 
ment's time,  the  little  animals  began  to  form  in  files  which  were 
fully  organised  in  five  minutes.  Tapping  the  ground  continually 
with  their  antennae,  they  took  up  their  larvae  and  moved  away  in 
order,  reconnoitering  the  territory  in  all  directions.  Not  a  pebble, 
not  a  crevice,  not  a  plant  was  left  unnoticed  or  overlooked.  The 
place  best  suited  for  concealing  their  young  was  very  soon  found, 
whereas  most  of  our  European  ants  under  such  conditions,  i.  e.,  in 
a  completely  unknown  locality,  would  probably  have  consumed  at 
least  an  hour  in  accomplishing  the  same  result.  The  order  and 


48  ANTS  AND  SOME  OTHER  INSECTS. 

dispatch  with  which  such  a  procession  is  formed  in  the  midst  of  a 
totally  strange  locality  is  almost  fabulous.  I  repeated  the  experi- 
ment in  two  localities;  both  times  with  the  same  result.  The  an- 
tennae of  the  Ecitons  are  highly  developed,  and  it  is  obvious  that 
their  brain  is  instinctively  adapted  to  such  rapid  orientation  in 
strange  places. 

In  Colombia,  to  be  sure,  I  had  had  opportunities  of  observing, 
not  the  temporary  nests,  but  the  predatory  expeditions  of  larger 
Ecitons  (£.  Burchelli  and  hamatum}  possessing  eyes.  But  these 
in  no  respect  surpassed  the  completely  blind  E.  carolinense  in  their 
power  of  orientation  and  of  keeping  together  in  files.  As  soon  as 
an  ant  perceives  that  she  is  not  being  followed,  she  turns  back  and 
follows  the  others.  But  the  marvellous  fact  is  the  certainty  of  this 
recognition,  the  quickness  and  readiness  with  which  the  animals 
recognise  their  topochemical  trail  without  hesitation.  There  is 
none  of  the  groping  about  and  wandering  to  and  fro  exhibited  by 
most  of  our  ants.  Our  species  of  Tapinoma  and  Polyergus  alone 
exhibit  a  similar  but  less  perfect  condition.  It  is  especially  inter- 
esting, however,  to  watch  the  perpetuum  mobile  of  the  antennas  of 
the  Ecitons,  the  lively  manner  in  which  these  are  kept  titillating 
the  earth,  all  objects,  and  their  companions. 

All  this  could  never  be  accomplished  by  a  tactile  sense  alone. 
Nor  could  it  be  brought  about  by  an  olfactory  sense  which  furnished 
no  spatial  associations.  As  soon  as  an  Eciton  is  deprived  of  its 
two  antennae  it  is  utterly  lost,  like  any  other  ant  under  the  same 
circumstances.  It  is  absolutely  unable  to  orient  itself  further  or  to 
recognise  its  companions. 

In  combination  with  the  powerful  development  of  the  cere- 
brum {corpora  pcduneulata}  the  topochemical  olfactory  sense  of  the 
antennae  constitutes  the  key  to  ant  psychology.  Feeling  obliged 
to  treat  of  the  latter  in  the  preceeding  lecture,  I  found  it  necessary 
here  to  discuss  in  detail  this  particular  matter  which  is  so  often 
misunderstood. 

[In  his  latest  Souvenirs  entomologiques  (Seventh  Series)  J.  H.  rabre  has 
recorded  a  number  of  ingenious  experiments  showing  the  ability  of  the  males  of 
Saturnia  and  Bombyx  to  find  their  females  at  great  distances  and  in  concealment. 


ANTS  AND  SOME  OTHER  INSECTS.  49 

He  tried  in  vain  (which  was  to  have  been  foreseen)  to  conceal  the  female  by  odors 
which  are  strong  even  to  our  olfactories.  The  males  came  notwithstanding.  He 
established  the  following  facts:  (i)  Even  an  adverse  wind  does  not  prevent  the 
males  from  finding  their  way  ;  (2)  if  the  box  containing  the  female  is  loosely  closed, 
the  males  come  nevertheless  ;  (3)  if  it  is  hermetically  closed  (e.  g.,  with  wadding  or 
soldered)  they  no  longer  come  ;  (4)  the  female  must  have  settled  for  some  time  on 
a  particular  spot  before  the  males  come  ;  (5)  if  the  female  is  then  suddenly  placed 
under  a  wire  netting  or  a  bell-jar,  though  still  clearly  visible,  the  males  neverthe- 
less do  not  fly  to  her,  but  pass  on  to  the  spot  where  she  had  previously  rested 
and  left  her  odor  ;  (6)  the  experiment  of  cutting  off  the  antennae  proves  very  little. 
The  males  without  antennae  do  not,  of  course,  come  again  ;  but  even  the  other 
males  usually  come  only  once  :  their  lives  are  too  short  and  too  soon  exhausted. 

At  first  Fabre  did  not  wish  to  believe  in  smell,  but  he  was  compelled  finally, 
as  a  result  of  his  own  experiments,  to  eliminate  sight  and  hearing.  Now  he  makes 
a  bold  hypothesis  :  the  olfactory  sense  of  insects  has  two  energies,  one  (ours), 
which  reacts  to  dissolved  chemical  particles,  and  another  which  receives  "physical 
odor-waves,"  similar  to  the  waves  of  light  and  sound.  He  already  foresees  how 
science  will  provide  us  with  a  "radiography  of  odors"  (after  the  pattern  of  the 
Roentgen  rays).  But  his  own  results,  enumerated  above  under  (4)  and  (5)  contra- 
dict this  view.  The  great  distances  from  which  the  Bombyx  males  can  discern 
their  females  is  a  proof  to  him  that  this  cannot  be  due  to  dissolved  chemical  par- 
ticles. And  these  same  animals  smell  the  female  only  after  a  certain  time  and 
smell  the  spot  where  she  had  rested,  instead  of  the  female  when  she  is  taken  away! 
This,  however,  would  be  inconceivable  on  the  theory  of  a  physical  wave-sense, 
while  it  agrees  very  well  with  that  of  an  extremely  delicate,  chemical  olfactory 
sense. 

It  is  a  fact  that  insects  very  frequently  fail  to  notice  odors  which  we  perceive 
as  intense,  and  even  while  these  are  present,  detect  odors  which  are  imperceptible 
to  our  olfactories.  We  must  explain  this  as  due  to  the  fact  that  the  olfactory  pa- 
pillae of  different  species  of  animals  are  especially  adapted  to  perceiving  very  differ- 
ent substances.  All  biological  observations  favor  this  view,  and  our  psycho-chem- 
ical theories  will  have  to  make  due  allowance  for  the  fact.] 


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